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Milner 
The  use  of  milk  as  food 


THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

LOS  ANGELES 


■■■■bHHHa 
•WHO  'liOiijao*? 
•AN  '•W130JAS 

•aui  -soaa  awoiAvs 

;  iNnovwiAvs  i 


I 


issued  July  14  1908. 


U.  S.  DEPARTMENT  OF  AGRICULTURE. 


FARMERS'   BULLETIN  363. 


STATE  NORMAL  SCHOOL 

LOS  ANGELES.  CAUit)RNlA 

THE  USE  OF  MILK  AS  FOOD. 


BY 

R.  D.  IMILNER,  PTtl.  B., 

Assistant  in    Nutritio?t  Investigations. 


rSEPARED  UNDER  THE  SUPERVISION  OF  THE  OFFICE  OF  EXPERIMENT  STATIONS, 
A.    C.    TRUE,    Director. 

Corrected  to  December  15, 1910, 


WASHINGTON: 

GOVERNMENT    PRINTING    OFFICE. 
1911. 


B5^ 


LETTER  OE  TRANSMITTAL 


U.  S.  Department  of  Agricultuke, 
Office  of  Experiment  Stations, 
Washington^  D.  C.yFebruary  12^  1900. 
Sir:  I  have  the  honor  to  transmit  herewith,  and  to  recommend 
for  publication  as  a  Farmers'  Bulletin,  an  article  on  the  use  of  milk 
as  food,  prepared  by  R.  D.  Milner,  of  this  Office,  which  summarizes 
the  results  of  numerous  experiments  carried  on  in  connection  with 
the  nutrition  investigations  of  the  Office  of  Experiment  Stations,  as 
well  as  data  gathered  from  publications  of  the  agricultural  experi- 
ment stations  and  general  sources. 

Perhaps  no  article  of  diet  is  more  important  than  milk,  and  the 
present  bulletin  discusses  such  questions  as  composition,  digestibility, 
care  of  milk  in  the  home,  use  of  milk  in  cookery,  and  its  economy 
as  compared  with  other  foods.  Some  general  information  is  also 
summarized  regarding  such  milk  products  as  butter,  cheese,  butter- 
milk, and  whey. 

The  present  bulletin  is  a  revision  and  extension  of  an  earlier 
Farmers'  Bulletin,  No.  74,  "  Milk  as  Food,"  which  it  is  designed  to 
replace. 

Respectfully,  A.  C.  True, 

Director. 
Hon.  James  Wilson, 

Secretary  of  Agriculture. 

3G3 


CONTENTS, 


Page. 

Introduction 7 

Sources  and  kinds  of  milk 8 

Composition  and  characteristics  of  milk 9 

The  protein  compounds  of  milk 10 

The  fats  and  carbohydrates  of  milk 11 

Mineral  matters  in  milk 11 

Bacteria  in  milk 11 

Specific  gravity  and  freezing  point  of  milk 12 

Variations  in  milk 13 

Flavor 14 

Dirt  in  milk 14 

Milk  as  the  possible  carrier  of  disease 15 

Preserving  milk 15 

Cold 16 

Heat 16 

Chemical  preservatives 17 

Condensed  milk  and  milk  powder 18 

Graded  and  certified  milk 19 

Care  of  milk  in  the  home 20 

Digestibility  of  milk 20 

Process  of  digestion 21 

Proportion  of  nutrients  digested 22 

Relative  value  of  cooked  and  raw  milk 23 

Milk  for  infants — Modified  milk — Homogenized  milk 25 

Special  infant  foods , 26 

Nutritive  value  of  milk  conipared  with  other  foods 27 

Nutritive  value  of  skim  milk 29 

Cost  of  nutrients  in  whole  milk  and  skim  milk 33 

The  use  cif  milk  in  cooking 35 

Milk  products 36 

Butter  and  cheese (^ 

Junket 38 

Cottage  cheese 38 

Cream 39)' 

Buttermilk 40 

Whey 40 

Sour  milk  or  clabber 40 

Kephir,  koumiss,  and  other  fermented  milk  products 41 

Summary 42 

363 

5 


ILLUSTRATIONS. 


Page. 

Chart  I.  Composition  and  fuel  value  of  milk,  milk  products,  and  other  foods. .  28 

II.  Composition  and  fuel  value  per  pound  of  milk  and  milk  products 30 

III.  Pecuniary  economy  of  milk  and  other  foods 34 

IV.  Composition  and  fuel  value  of  some  milk  products 37 

303 

6 


THE  USE  OF  MILK  AS  FOOD. 


INTRODUCTIOlf. 

According  to  the  census  of  1900,  about  two-tliirds  of  all  the  niilk 
produced  for  sale  by  the  farmers  of  the  United  States  was  used  to  make 
butter  and  cheese,  while  the  remaining  third  was  consumed  directly 
as  milk  and  cream.  The  figures  given  showed  that  on  the  average 
each  person  in  this  country  consumed  about  20  gallons  of  milk  a 
year,  or  that  each  family  of  five  used  about  1  quart  a  day.  Accord- 
ing to  estimates  of  the  Bureau  of  xVnimal  Industry  of  this  Depart- 
ment, the  average  annual  consumption  in  1903  was  about  30  gallons 
per  person.  This  Department  has  previously  published  bulletins 
which  discuss  the  various  phases  of  the  milk  question  as  they  appear 
to  the  farmer  who  produces  it,  the  dealer  who  distributes  it,  and  the 
manufacturers  of  butter  and  cheese.  The  purpose  of  the  present 
article  is  to  consider  the  question  of  milk  as  a  food  from  the  point 
of  view  of  the  consumer,  to  show  why  it  is  a  valuable  part  of  his 
diet,  and  under  what  conditions  it  is  most  valuable.  The  importance 
of  such  a  consideration  is  indicated  by  the  fact  that  milk  and  cream 
together  furnish  16  per  cent  of  the  total  food  of  the  average  American 
family. 

Questions  pertaining  to  the  care  and  management  of  dairy  cows, 
the  effect  of  different  systems  of  feeding  on  the  yield  and  quality  of 
milk,  the  distribution  and  marketing  of  milk,  the  manufacture  of 
butter,  cheese,  and  other  dairy  products,  and  related  questions  have 
been  studied  at  the  agricultural  experiment  stations  of  the  United 
States  and  elsewhere.  The  Dairy  Division  of  the  Bureau  of  Animal 
Industry  of  this  Department  has  carried  on  extensive  investigations 
of  a  great  many  problems  of  milk  and  its  products,  and  to  their  work 
much  of  the  data  at  present  available  may  justly  be  attributed.  The 
study  of  the  digestibility  and  nutritive  value  of  milk  and  its  products 
has  formed  a  part  of  the  cooperative  nutrition  investigations  carried 
on  under  the  auspices  of  the  Office  of  Experiment  Stations,  and  many 
facts  which  are  of  interest  and  importance  have  been  secured.  In 
the  following  pages  information  drawn  from  this  and  similar  sources 
has  been  summarized. 

363 


THE   USE    OF    MILK   AS   FOOD. 


SOURCES  AND  KINDS  OF  MILK. 


In  civilized  countries  where  the  climate  allows,  cows  have  been 
most  generally  bred  for  the  piirj^ose  of  giving  milk,  probabh'  not 
so  much  because  their  milk  was  more  particularly  desirable  for 
human  food  than  that  of  some  other  mammals  as  because,  all  things 
considered,  they  can  be  made  to  give  the  best  results  for  a  given 
amount  of  care  and  feed.  Our  preference  for  their  milk  is  un- 
doubtedly the  result  of  habit  and  acquired  taste  rather  than  of  any 
intrinsic  superiority,  save,  of  course,  as  special  breeding  has  de- 
veloped certain  desirable  characteristics.  In  some  parts  of  the  world 
other  kinds  of  milk  are  used ;  goat's  milk  is  very  common,  especially 
in  the  rough,  hilly  districts  of  Europe;  buffalo's  milk  is  much  used 
in  India,  and  llama's  milk  in  South  America,  while  camel's  milk  is 
esteemed  in  desert  countries,  and  mare's  milk  on  the  steppes  of  Russia 
and  Central  Asia.  Sheep's  milk  is  used  in  Europe  and  elsewhere 
for  making  certain  kinds  of  cheese  and  in  other  ways,  and  the  milk 
of  reindeers  is  commonly  used  as  food  in  the  arctic  regions.  So 
much  does  cow's  milk  predominate  in  the  western  world,  however, 
that  unless  otherwise  specified  the  word  milk  almost  always  refers 
to  that  kind. 

Perhaps  no  food  has  been  more  often  studied  by  chemists  than 
milk  and  its  products,  and  so  a  great  deal  of  information  is  available 
regarding  the  composition  and  properties  of  these  important  food 
materials. 

The  average  composition  of  cow's  and  some  other  kinds  of  milk 
used  for  food  is  given  in  the  table  which  follows: 


Average  composition  of  milk  of  various  kinds. 


Kind  of  milk. 

Water. 

Total 
solids. 

Protein. 

Fat. 

Carbo- 
hydrates 
(milk 
sugar). 

Mineral 
matters. 

Fuel 
value 

Casein. 

Albumin. 

Total. 

per 
pound. 

Per  cent. 
87.58 
87.27 
86.88 
83.57 
82.  IG 
86.13 
87.13 
86. 55 
67.20 
90. 58 
90.12 

Per  ct. 
12.6 
12.8 
13.1 
16.4 

Per  ct. 
0.80 
2.88 
2.87 
4.17 
4.26 

Per  cent. 
1.21 
.51 
.89 
.98 
.46 

Per  ct. 
2.01 
3.39 
3.76 
5.15 

""'3.' 63" 

Per  cent. 
3.74 
3.68 
4.07 
6.18 
7.61 
4.80 
2.87 
3.15 
17.09 
1.14 
1.37 

Per  cent. 
6.37 
4.94 
4.64 
4.73 
4.77 
5.34 
5.39 
5.60 
2. 82 
6.87 
6.19 

Per  cent. 

0.30 
.72 
.85 
.96 
.84 
.70 
.74 
.80 

1.49 
.36 
.47 

Calories. 
310 

Cow 

310 

Goat 

315 

410 

Buffalo  (Indian)  ... 
Zebu 

'""'9.'9' 
10.4 

3.49 
3.00 
8.38 
1.30 
.79 

.38 

.90 
1.51 

.75 
1.06 

Ass 

2i5 

As  the  figures  in  the  table  make  plain,  milk  of  all  sorts  is  a  dilute 
food,  as  it  contains  a  large  percentage  of  water,  the  lowest  proportion 
according  to  the  figures  cited  being  noted  with  reindeer  milk  and 
the  highest  wuth  mare's  milk.     The  three  groups  of  protein,  fat,  and 

363 


THE   USE   OF   MILK   AS   FOOD.  9 

carbohydrates  are  represented  by  fair  proportions,  the  quantities  of 
protein  and  fat  being  especially  noteworthy,  as  it  is  these  constituents 
and  the  mineral  matt^n-  or  ash  which  to  a  large  degree  give  milk 
its  peculiar  value  as  a  food  for  young  mammals. 

COMPOSITION  AND  CHARACTERISTICS  OF  MILK. 

In  the  discussion  of  the  composition  and  characteristics  of  milk 
which  follows,  reference  is  made  almost  exclusively  to  cow's  milk. 
as  this  is  the  only  kind  which  is  especially  important  in  diet  in  the 
United  States,  at  least  after  infancy.  From  the  large  number  of 
analyses  of  milk  and  milk  products  which  have  been  reported  by 
the  agricultural  experiment  station  chemists  and  other  investigators 
the  following  data  showing  the  average  composition  of  these  mate- 
rials have  been  compiled.  The  table  also  includes,  for  purposes  of 
comparison,  the  average  composition  of  a  number  of  other  common 
food  materials. 

Average  composition  of  milJc  products  and  other  food  materials. 


Material. 


Vv'hole  milk 

Skim  milk 

Cream 

Buttermilk 

Whey 

Condensed  milk,  unsweetened 

Condensed  milk,  sweetened 

Butter 

Cheese,  American  Cheddar 

Cheese,  cottivge 

Cheese,  Swiss 

Milk  powder  (from  skimmed  milk) 

Kephir 

Koumiss 

Infant  and  invalid  foods,  farinaceous 

Infant  and  invalid  foods  containing 
milk  and  starches 

Infant  and  invalid  foods,  malted  prepa- 
rations   

Beef,  sirloin  steak 

Eggs,  as  purchased 

Wheat  flour,  patent  roller  process 

Wheat  bread,  white 

Beans,  baked 

Potatoes,  as  purchased 

Apples,  as  purchased 


Refuse. 


Per  cent. 


12.8 
H.2 


20.0 
25.0 


Water. 


Per  cent. 
87.0 
90.6 
74.0 
91.0 
93.0 
71.3 
26.0 
13.0 
33.5 
53.0 
31.4 

3.0 
89.6 
90.7 

9.4 

4.3 

4.2 
64.0 
65.5 
12.0 
35.3 
68.9 
62.6 
63.3 


Protein. 


Per  cent. 

3.3 

3.4 

2.5 

3.0 

1.0 

7.4 

8.2 

1.0 

26.0 

19.6 

27.6 

34.0 

3.1 

2.2 

9.4 

9.6 

12.0 

16.5 

11.9 

11.4 

9.2 

.    6.9 

1.8 

.3 


Fat. 


Per  cent. 

4.0 

.3 

18.5 

.5 

.3 

8.5 

9.6 

83.0 

36.5 

23.2 

34.9 

3.1 

2.0 

2.1 

.4 

3.8 

1.0 

16.1 

9.3 

1.0 

1.3 

2.5 

.1 

.3 


Carbohy- 
drates. 


Per  cent. 
b-.O 
5.1 
4.6 
4.8 
6.0 
11.1 
54.3 


1.5 

2.1 

1.3 

51.9 

o4.5 

6  4.1 

C79.9 


«79.8 


75.1 
53.1 
19.6 
14.7 
10.8 


Per 


cent. 
0.7 

!5 

.7 

.7 

1.7 

1.9 

3.8 

3.5 

2.1 

4.8 

8.0 

.8 


3.0 

.9 

.9 

.5 

1.1 

2.1 


"  Including  2.1  per  cent  alcohol  and  0.8  per  cent  lactic  acid. 
'  Including  1.7  per  cent  alcohol  and  0.0  per  cent  lactic  acid. 
"  Including  6.62  per  cent  soluble   carbohydrates    (sugars). 
''Including  49.05  per  cent  soluble  carbohydrates    (sugars). 
«  Including  4S.39  per  cent  soluble  carbohydrates    (sugars). 

Milk  as  it  is  drawn  from  the  cow  is  familiar  to  all  as  an  opaque, 
whitish  liquid,  which  varies  considerably  in  appearance  and  in  flavor. 
It  is  commonly  described  as  consisting  of  a  thin,  bluish-white,  some- 
what transparent  liquid,  called  the  plasma,  in  which  are  floating  yel- 
lowish globules  of  fat  so  numerous  and  so  well  distributed  that  the 
whole  appears  to  be  a  white  fluid.    The  chief  bulk  of  milk  is  water, 

71701°— Rull.  308—11 2 


10  THE   USE   OF   MILK   AS   FOOD. 

the  amount  of  which  may  vary,  even  in  ordinary  unadulterated  milk, 
from  90  per  cent  in  a  very  poor  product  to  84  per  cent  in  an  unusually 
rich  milk,  the  average  being,  as  appears  from  the  data  in  the  table, 
about  87  per  cent.  The  corresponding  solid  matter  varies  from  10  to 
16  per  cent.  This  solid  matter,  or  "  total  nutrients,"  is  made  up  of 
protein,  fats,  carbohydrates,  and  mineral  matter.  The  proportion  of 
these  vary  within  certain  limits ;  but,  roughly  speaking,  one-twentieth 
of  the  total  solids  are  mineral  substances,  one-fourth  protein,  three- 
tenths  fat,  and  four-tenths  carbohydrates,  as  the  above  table  shows. 

THE  PROTEIN   COMPOUNDS   OF   MILK. 

Protein  compounds  are  the  important  nitrogenous  ingredients  which 
are  indispensable  in  the  formation  of  body  tissues  and  fluids;  they 
may  also  be  burned  in  the  body  to  furnish  energy,  their  fuel  value 
being  about  equal  to  that  of  the  carbohydrates  and  less  than  half  as 
great  as  that  of  the  fats.**  Protein  is  found  in  different,  forms,  such 
as  the  Avhite  of  egg  (egg  albumin),  the  lean  of  meat  (myosin),  the 
legumin  of  peas  and  beans,  etc.  In  milk  the  principal  protein  com- 
pound is  casein.  In  chemical  composition  the  casein  differs  fi*om  the 
other  protein  compounds  of  milk  in  that  it  contains  both  phosphorus 
and  sulphur.  Wlien  acid  is  added  to  a  solution  of  this  casein,  it  is  pre- 
cipitated in  light,  white  flakes,  such  as  are  seen  in  sour  milk.  If,  how- 
ever, an  alkali  such  as  limewater  is  also  added  to  neutralize  the  acid, 
these  curds  do  not  form  or  are  redissolved.  Another  kind  of  pre- 
cipitation or  curdling  of  the  casein  occurs  when  rennet  is  added,  as 
in  cheese  making.  The  ferment  rennin,  which  is  present  in  rennet 
(and  also  in  human  gastric  juice),  throws  down  the  casein,  but  into 
a  tougher  and  less  flocculent  or  flaky  mass  than  the  acid,  and  ono 
which  can  not  be  redissolved  by  the  addition  of  an  alkali.  Besides 
the  casein  there  is  a  certain  amount  of  albumin  present  in  milk,  some- 
times called  lactalbumin,  but  the  quantity  is  verj'^  much  smaller  than 
that  of  the  casein,  being  on  the  average  about  one-seventh  of  the 
total  protein.  The  proportion  of  albumin  to  casein  varies  in  the  milk 
of  different  kinds  of  animals  and  also  in  the  milk  of  a  single  cow. 
There  are  other  nitrogenous  substances  occurring  in  milk,  but  in  such 
small  quantities  that  they  need  not  be  considered  here. 

The  total  protein  of  milk  should  not  vary  in  any  great  degree,  and 
will  average  not  far  from  3.3  per  cent  of  the  whole  milk,  or  about  25 
per  cent  of  the  total  solids. 

<»  The  fuel  value  of  any  substance  is  artificially  determined  by  burning  it  in  a 
bomb  calorimeter  and  measuring  the  beat  given  off.  The  unit  of  measure  is  a 
caloric,  wliich  represents  the  amount  of  heat  necessary  to  raise  the  temperature 
of  1  poimd  of  water  4°  F.  One  pound  of  protein  or  carbohydrates  has  a  fuel 
value  of  1,820  calories,  and  1  ix)und  of  fats  4,040  calories. 
363 


THE   USE    OF   MILK   AS   FOOD.  H 

THE  FATS  AND  CARBOHYDBATES  OF  MILK. 

The  fat  of  milk  is  commercially  the  most  important  of  its  con- 
stituents, since  it  is  the  source  of  butter  and  enters  largely  into  the 
composition  of  cheese.  It  is  found  throughout  the  milk  in  globules, 
varying  in  size  in  the  milk  from  different  animals,  which,  being 
lighter  than  water,  tend  to  rise  to  the  top  of  the  milk  as  it  stands, 
forming  the  cream.  Chemically  speaking,  the  fat  of  milk,  commonly 
called  butter  fat,  consists  of  several  different  fats,  the  chief  of  which, 
called  stearin,  palmitin,  and  olein,  are  the  same  as  those  that  make  up 
the  bulk  of  meat  fat  (tallow,  lard,  etc.),  as  well  as  of  many  vegetable 
fats.  The  amount  and  quality  of  fat  in  milk  varies  widely,  for  rea- 
sons which  are  mentioned  later.  The  amount  should  not  fall  below 
3  per  cent,  and  except  in  unusually  rich  milk  will  not  exceed  5  jjcr 
cent.  It  averages  about  4  per  cent  of  the  milk,  or  about  31  per  cent 
of  the  total  of  solids. 

The  chief  carbohydrate  which  occurs  in  milk  is  lactose  or  milk 
sugar.  It  is  similar  in  chemical  composition  to  cane  sugar,^but  is 
not  as  readily  soluble,  and  this  is  one  reason  at  least  why  it  does  not 
taste  as  sweet,  though  tests  made  with  solutions  show  that  cane  sugar 
is  markedly  superior  as  regards  this  property.  It  may  be  obtained 
in  crystals,  but  milk  sugar  is  usually  marketed  as  a  fine  white  powder 
much  like  confectioners'  sugar  in  appearance,  and  is  largely  used 
by  pharmacists  and  j)hysicians  as  a  vehicle  for  drugs  in  the  manu- 
facture of  powders,  pills,  tablets,  etc.  The  amount  of  milk  sugar  in 
cow's  milk  varies  from  4  to  G  per  cent,  the  average  being  about  5  per 
cent  of  the  total  milk,"  or  38  per  cent  of  the  total  solids. 

The  milk  sugar  remains  in  the  whey  when  casein  or  curd  is  removed 
in  cheese  making,  and  may  be  readil}^  recovered.  The  manufacture 
of  milk  sugar  from  whey  is  an  important  industry. 

MINERAL  MATTERS  IN  MILK. 

The  ash  constituents  in  milk  consist  mainly  of  the  phosphates  and 
chlorids  of  soda,  potash,  and  lime.  Most  of  these  are  dissolved  in 
the  plasma,  but  tiny  particles  of  the  phosphates  of  lime  remain  un- 
dissolved, and  are  said  to  be  a  cause  of  the  bluish  tint  found  in  milk. 
The  mineral  matters  make  up  about  seven-tenths  of  1  per  cent  of  the 
whole  milk  or  5  per  cent  of  the  solid  matter.  Along  with  these  prin- 
cipal ingredients  milk  also  contains  minute  quantities  of  other  sub- 
stances, some  of  which  will  be  referred  to  later. 

BACTERIA  IN   MILK. 

Besides  the  chemical  compounds,  milk  also  contains  large  numbers 
of  minute  organisms  called  bacteria.     Few,  if  any,   are  normally 

363 


12  THE   USE    OF    MILK   AS    FOOD. 

present  in  the  milk  within  the  udders  of  clean,  healthy  cows,  but  they 
are  so  abundant  everywhere  in  the  air,  especially  about  the  stable  and 
barnyard,  and  cling  in  such  numbers  to  the  bodies  of  the  cows,  that 
they  are  almost  always  found  in  milk  as  soon  as  it  leaves  the  udders 
or  even  just  inside  the  teats.  They  reproduce  very  rapidly  in  a 
favorable  medium,  such  as  warm  milk,  so  that  the  number  present 
becomes  very  large  unless  measures  are  taken  to  hinder  their  increase. 
The  amount  in  milk  of  a  given  age  of  course  varies  with  the  condi- 
tions; that  from  clean  cows,  with  freshly  washed  udders,  milked 
into  well-scalded  pails,  in  a  clean  place,  free  from  air  currents,  by 
persons  with  clean  hands  and  clothes,  and  quickly  cooled  and  care- 
fully handled,  mny  contain  very  few,  while  milk  from  ill-kept 
animals  untidily  handled  in  a  dirty  place  may  contain  enormous 
quantities.  Since,  as  will  be  shown  later,  bacteria  cause  the  spoiling 
of  milk,  and  may  be  harmful  in  other  ways,  it  is  very  evident  that 
scrupulous  cleanliness  about  everything  which  comes  in  contact 
with  the  milk  is  of  first  importance. 

A  great  many  kinds  of  bacteria  have  been  found  in  milk,  each  of 
which  occasions  a  special  set  of  changes  as  it  develops.  Perhaps  the 
most  important  kinds  are  those  which  cause  the  ordinary  souring  of 
milk  and  are  the  first  to  produce  any  noticeable  change  in  the  taste 
and  odor.  In  their  growth  they  feed  upon  the  milk  sugar  and  con- 
vert it  into  lactic  acid,  which  gives  slightly  soured  milk  its  peculiar 
taste  and  odor.  When  enough  of  this  lactic  acid  has  formed  it  acts 
upon  the  casein,  causing  it  to  separate  into  loose,  light  flakes  such 
as  we  see  in  ordinary  sour  "  lobbered  "  milk.  Other  bacteria  may 
also  develop  in  sour  milk  which  give  it  a  strong,  unpleasant  odor  or 
flavor.  Some  of  the  products  of  bacterial  action  on  milk  are  desir- 
able— for  instance,  those  which  give  to  butter  and  cheese  the  character- 
istic flavors  and  odors.  Still  others  occasionally  apj^car  in  milk 
which  color  it  very  brightly  or  give  it  a  slimy  or  ropy  consistency. 
Milk  sometimes  sours  more  quickly  than  ordinarily  when  there  is  a 
thunderstorm.  This  is  often  said  to  be  due  to  electricity  in  the  air, 
but  bacteriologists  claim  that  it  is  due  to  the  hot,  damp  atmosphere 
which  usually  precedes  the  storm,  as  the  heat  is  especially  favorable 
to  the  growth  of  bacteria. 

SPECIFIC   GRAVITY  AND   FREEZING  POINT   OF   MILK. 

Milk  is  slightly  heavier  than  water,  its  specific  gravity  ranging 
from  1.029  to  1.034  at  60°  F.  This  means  that  while  a  quart  of  water 
weighs  2  pounds  1.333  ounces,  a  quart  of  milk  weighs  from  1.029  to 
1.034  times  as  much,  or  not  far  from  2  pounds  2.5  ounces.  The  spe- 
cific gravity  depends  upon  the  proportion  of  water  and  other  sub- 
stances.    Since  the  fat  is  lighter  than  water,  the  richer  the  milk  is  in 

363 


THE   USE   OF   MILK   AS   FOOD!  13 

butter  fat  the  lower  its  specific  gravity,  provided,  of  course,  that  the 
other  solids  are  not  increased  proportionally.  It  follows  also  that 
the  removal  of  the  fat  increases  the  specific  gravity,  so  that  skim  milk 
has  a  specific  gravity  of  from  1.033  to  1.037.  On  the  other  hand,  the 
addition  of  water  to  skimmed  milk  brings  down  the  specific  gravity. 
The  freezing  point  of  milk  also  varies  with  the  composition,  falling 
as  the  proportion  of  solids  increases  and  rising  if  water  is  added.  In 
average  milk  it  is  about  31°  F.  This  factor  is  of  importance  in  judg- 
ing of  the  purity  of  milk. 

VABIATIONS   IN   MILK. 

The  milk  which  is  ordinarily  sold  for  household  use  is  subject  to 
considerable  variatit^n  in  composition,  and  it  is  entirely  possible  for 
one  man  to  pay  nearly  twice  as  much  as  his  neighbor  for  an  equiva- 
lent nutritive  value  in  milk  at  the  same  price  per  quart  but  from  dif- 
ferent dealers.  It  is  owing  to  such  natural  variation  in  composition 
that  milk  is  purchased  at  creameries  on  the  basis  of  its  fat  content. 
(See  p.  19.)  This  variation  in  nutritive  value  is  in  large  part  attrib- 
utable to  differences  in  the  breeds  of  cows  kept,  certain  breeds  pro- 
ducing milk  which  contains  more  fat  than  others.  Among  the  best 
for  producing  cream  are  the  Channel  Islands  breeds,  which  give  a 
milk  rich  in  large  fat  globules,  that  rise  easily  to  the  surface.  For 
general  purposes,  however,  breeds  which  yield  milk  containing  fairly 
good  proportions  of  all  the  ingredients  of  the  solids  are  considered 
more  desirable.  The  age  of  the  animal  also  has  considerable  influ- 
ence, young  cows  producing  richer  milk  than  old  ones  of  the  same 
kind.  In  general  a  well-fed  cow  gives  more  and  better  milk  than  if 
poorly  fed,  but  the  relative  proportions  of  fat,  casein,  and  sugar  in 
the  milk  are  not  so  greatly  influenced  by  the  composition  of  the  food 
as  is  the  quantity  of  milk.  The  average  cow  of  a  given  breed  pos- 
sesses certain  capabilities  for  producing  milk,  but  does  not  reach  her 
normal  capacity  of  milk  production  unless  she  is  well  fed.  AVlien 
once  she  has  a  sufficient  and  well-balanced  ration,  neither  the  compo- 
sition nor  the  amount  of  the  milk  yield  seems  to  be  greatly  improved 
by  either  increasing  the  ration  or  changing  the  proportion  of  the 
nutrients  it  supplies. 

The  milk  flow  of  a  given  cow  is  usually  largest  soon  after  calving ; 
as  the  period  of  lactation  progresses  the  milk  flow  gradually  falls  off, 
and,  as  a  rule,  the  milk  grows  richer,  i.  e.,  the  proportion  of  solids  in- 
creases. The  proportion  of  fat  to  the  other  solids  in  the  milk  of  a 
given  cow  varies  from  day  to  day  and  from  milking  to  milking. 

On  account  of  all  these  variations  in  the  milk  of  individual  cows, 
dairymen  who  supply  the  milk  trade  usually  find  it  best  to  mix  the 
milk  from 'all  the  cows  in  the  herd  immediately  after  it  is  drawn. 

363 


14  THE   USE   OF   MILK  AS   FOOD. 

This  is  of  considerable  advantage  to  the  consumer,  as  it  makes  the 
milk  much  more  uniform  from  day  to  day. 

A  cause  of  variation  in  milk  is  found  in  the  adulteration  not  infre- 
quently practiced  by  unprincipled  producers  or  dealers.  The  chief 
methods  of  adulteration  aside  from  the  use  of  chemical  preservatives 
are  the  addition  of  water  and  the  removal  of  a  portion  of  the  fat, 
both  methods  being  often  used  together.  These  methods  are  not  only 
fraudulent  as  regards  money  value,  but  also  diminish  the  food 
value.  The  specific  gravity  of  the  milk  is  sometimes  used  as  a  test 
of  its  purity,  but  since  removing  part  of  its  fat  in  the  form  of  cream 
raises  and  adding  water  lowers  the  specific  gravity,  one  form  of 
adulteration  may  cover  up  the  other,  and  thus  render  this  test  alone 
unreliable.  A  similar  difficulty  is  found  in  testing  milk  by  its  freez- 
ing point,  which  varies  with  the  proportion  of  the  different  soluble 
constituents. 

FLAVOR. 

The  flavor  of  milk  varies  almost  as  much  as  its  composition.  It  is 
in  part  due  to  the  amount  of  fat  present,  but  also  to  the  number  and 
kind  of  bacteria,  or  rather  to  the  product  of  bacterial  action.  The 
flavor  is  also  often  influenced  by  the  food  of  the  cow ;  this  is  especially 
noticeable  when  the  cows  have  eaten  some  strong-tasting  substance, 
such  as  turnips,  and  is  due  to  the  fact  that  the  volatile  oil  or  other 
flavor  of  the  food  passes  directly  through  the  animal  tissues  into  the 
milk.  Milk  also  absorbs  flavors  and  odors  from  the  air  much  more 
quickly  than  most  foods.  The  "  animal "  or  "  cowy  "  taste  and  smell, 
which  are  often  noticeable  in  new  milk,  are  believed  to  be  due  in  part 
to  this  absorption.  It  may  also  be  due  in  part  to  stable  dirt  which 
accidentally  falls  into  the  milk.  The  cleaner  the  animal  the  less 
noticeable  is  this  taste  in  milk.  It  may  be  considerably  lessened  by 
promptly  cooling  and  aerating  the  milk  after  it  is  drawn. 

A  pan  of  milk  kept  in  a  closed  ice  box  with  fish  or  high-flavored 
vegetables  or  fruit  is  very  likely  to  acquire  flavor  and  odor  from 
them ;  hence  milk  sliould  be  kept  where  the  air  is  free  from  such  taint. 

DIRT   IN  MILK. 

There  is  frequently  more  or  less  dirt  in  freshly  drawn  milk,  most 
of  it  fine  particles  of  litter  and  manure  which  fall  into  the  pail  from 
the  body  of  the  cow.  Milk  should  always  be  strained  directly  the 
milking  is  over,  or,  better  still,  it  should  be  drawn  into  pails  covered 
with  straining  cloths;  but  even  with  these  precautions  some  dirt  may 
be  present.  Of  course,  the  amount  varies  Avith  the  condition  in  Avhich 
the  cow  and  her  surroundings  are  kept ;  under  ideal  dairy  conditions 
only  very  small  quantities  are  found,  while  milk  from  untidy  estab- 

363 


THE   USE   OF   MILK   AS   FOOD.  15 

lisliments  may  contain  enough  in  a  quart  to  form  a  noticeable  sedi- 
ment. Milk  with  enough  dirt  to  be  visible  indicates  a  badly  kept 
dairy  and  should  not  be  tolerated,  and  consumers  should  always  insist 
upon  having  clean  milk.  It  should  be  remembered  that  the  visible 
dirt  does  not  tell  the  whole  story ;  some  of  the  manure  that  falls  into 
milk  is  dissolved,  and  is  no  longer  noticeable  to  the  eye. 

If  milk  is  measured  out  from  a  large  can  at  the  door  of  each  cus- 
tomer dust  and  dirt  from  the  street  as  well  as  bacteria  may  get  into 
it.  The  custom  of  delivering  it  in  sealed  bottles  is  much  neater  and 
has  the  further  advantage  of  giving  the  buyers  more  uniform 
amounts  of  cream  than  where  some  get  the  top  and  some  the  bottom 
of  the  milk  taken  from  a  large  can. 

MILK   AS   THE   POSSIBLE   CARRIEB,   OE   DISEASE. 

Disease  germs  may  get  into  milk  either  directly  from  a  diseased 
cow  or  indirectly  from  an  infected  person,  from  polluted  water,  or 
in  some  similar  way.  The  most  dreaded  disease  w4iich  may  come 
directly  from  the  cows  is  tuberculosis.  It  is  certain  that  the  tubercle 
bacillus,  the  germ  which  causes  the  disease,  does  sometimes  exist 
in  milk  from  tuberculous  animals ;  whether  or  not  persons  who  drink 
such  milk  may  become  infected  by  it  is  extremely  hard  to  prove. 
There  are  many  other  possible  sources  of  contagion,  and  the  disease 
develops  so  slowly  that  by  the  time  it  is  recognized  it  is  usually  too 
late  to  trace  the  cause.  Nevertheless,  there  is  quite  enough  evidence 
that  the  disease  may  be  carried  in  this  way  to  make  the  use  of  milk 
from  tuberculous, cows  too  dangerous  to  be  tolerated,  even  when  the 
animals  are  only  slightly  diseased.  Among  the  contagious  diseases 
to  which  the  cows  are  not  liable  but  which  may  be  spread  by  milk 
the  most  common  are  perhaps  scarlet  fever,  typhoid  fever,  and 
diphtheria.  Statistics  show  that  milk  is  very  often  the  cause  of  an 
epidemic  of  such  contagious  disease,  and  not  infrequently  a  serious 
epidemic  may  be  traced  to  the  milk  from  a  single  farm.  The  bacteria 
causing  these  diseases  frequently  enter  the  milk  from  contaminated 
water  used  in  washing  milk  utensils,  etc.,  or  from  persons  who  have 
been  exposed  to  disease  and  who  handle  the  milk.  For  this  reason  no 
water  which  is  not  above  suspicion  should  be  used  about  the  dairy 
(or  anywhere  else)  for  either  drinking  or  washing,  and  no  person 
who  has  been  exposed  in  any  way  to  such  diseases  should  be  allowed 
about  the  cows,  the  milk,  or  the  milk  utensils. 

PRESERVING  MILK. 

If  milk  could  be  obtained  and  kept  free  from  bacteria  it  would 
probably  remain  sweet  almost  indefinitely.  Hoav  near  to  this  ideal 
it  is  possible  to  come  may  be  seen  from  the  fact  that  milk  from  several 

363 


16  THE   USE   OF   MILK   AS   FOOD. 

American  dairies  exhibited  at  the  Pai'is  Exposition  in  1900  was  sweet 
when  over  two  weeks  old,  no  method  of  preservation  being  followed 
except  cleanliness  and  keeping  it  at  a  temperature  of  10°  to  42°  F. 
According  to  more  recent  data,  published  by  the  Bureau  of  Animal 
Industry  of  this  Department,  clean  milk  may  be  kept  five  to  seven 
weeks."  The  conditions  which  make  such  milk  possible  are  still  un- 
common, but  they  are  becoming  and  will  continue  to  become  more 
common  as  consumers  realize  that  it  is  worth  the  extra  cost  which  the 
necessary  carefulness  entails.  At  present,  however,  it  is  often  neces- 
sary to  find  some  means  of  checking  the  growth  of  the  bacteria. 
Besides  the  various  methods  of  drying  milk,  which  will  be  discussed 
later  (see  p.  18),  there  are  three  means  of  accomplishing  this:  (1) 
By  cold,  (2)  by  heat,  and  (3)  by  the  use  of  chemical  preservatives. 

COLD. 

Low  temperature,  even  when  extreme,  does  not  of  itself  kill  bac- 
teria, but  any  temperature  below  50°  F.  makes  them  more  or  less  in- 
active for  the  time  being.  Occasionally  milk  is  preserved  by  freezing, 
but  this  is  undesirable  because  the  character  of  the  ingredients  is 
slightly  altered  by  the  process.  The  changes  begin  at  about  35°  F., 
and  milk  should  not  ordinarily  be  kept  at  a  lower  temperature  than 
this.  Down  to  that  point,  however,  the  cooler  the  milk  the  better  it 
keeps.  As  has  been  suggested,  milk  should  be  cooled  as  soon  as  it  is 
drawn,  in  order  that  bacteria,  whose  growth  is  very  rapid,  may  not 
make  too  much  headway  in  the  warm  liquid. 

HEAT. 

Slight  warmth  is  very  favorable  to  the  growth  of  bacteria,  but  great 
heat  is  fatal  to  them.  Unfortunately,  heat  sufficient  to  destroy  all  the 
varieties  also  causes  changes  in  the  chemical  composition  and  flavor 
of  the  milk,  as  seen  in  boiled  milk;  otherwise  cooking  milk  would 
be  a  very  simple  and  satisfactory  way  of  preserving  it.  "When  heat 
is  used,  it  is  well  to  apply  it  in  such  a  way  as  to  do  the  most  damage 
to  the  bacteria  with  the  least  damage  to  the  other  materials.  The 
two  most  common  methods  are  pasteurization  and  sterilization.  These 
terms  are  often  used  interchangeably,  but  they  really  refer  to  distinct' 
processes. 

In  pasteurizing  milk  the  aim  is  to  destroj'^  as  many  bacteria  as 
possible  without  producing  any  of  the  changes  in  the  chemical  con- 
stituents which  take  place  when  the  milk  is  heated  and  which  begin 
at  about  1G7°  F.  Experience  has  shown  that  the  temperature  of 
milk  during  pasteurization  should  not  exceed  185°  F.  nor  fall  below 

«  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.  Circ.  117. 
363 


THE   USE    OF    MILK   AS   FOOD.  IT 

140°  F.  To  pasteurize  milk  it  may  be  placed  in  air-tight  bottles  or 
bottles  which  are  stoppered  with  sterilized  cotton,  and  immersed  to 
the  neck  in  hot  water  and  heated,  for  instance,  at  149''  F.  for  a  half 
hour  or  at  167°  F.  for  lifteen  minutes,  and  then  quickly  cooled  to 
50°  F.  or  less.  This  rapid  cooling  lessens  the  "  cooked  "  taste  so 
objectionable  to  many  persons. 

Sterilized  milk,  on  the  other  hand,  is  milk  subjected  to  heat  suf- 
ficient to  destroy  all  the  organisms  in  it.  It  is  not  always  accom- 
j)lished  by  simply  boiling  the  milk  unless  the  boiling  is  repeated  on 
two  or  three  successive  days.  Higher  temperatures  than  the  boiling 
jDoint  are  necessary  to  assure  sterilization  or  the  complete  destruction 
of  all  organisms  at  one  application  of  heat  of  fifteen  to  thirty  min- 
utes' duration.  For  many  practical  purposes,  however,  simply  rais- 
ing the  milk  to  the  boiling  point  is  sufficient.  Much  of  the  so-called 
"  sterilized  milk  ''  has  been  thus  treated  and  is  by  no  means  free  from 
living  organisms.  Sterilized  milk  will  remain  sweet  in  a  warm  place 
longer  than  pasteurized,  but  the  greater  heat  produces  more  of  the 
undesirable  chemical  changes.  Both  pasteurized  and  sterilized  milk 
should  be  kept  in  clean,  air-tight  bottles  or  new  bacteria  will  enter 
and  begin  their  destructive  work. 

Pasteurized  milk  can  now  be  obtained  in  many  large  milk  depots; 
but  under  ordinary  conditions  housekeepers  usually  prefer  to  buy 
fresh  milk  and  do  their  own  heating  when  necessary.  Pasteurized 
cream  is  frequently  sold,  but  is  considered  less  desirable  than  fresh. 
It  seems  thinner  and  does  not  "whip"  well  (see  p.  39).  These  dif- 
ferences do  not  necessarily  mean  that  the  pasteurized  cream  contains 
less  fat  than  the  fresh,  but  that  the  heat  has  somewhat  changed  the 
character  of  the  fat  globules. 

CHEMICAL   PEESEBVATIVES. 

These  are  substances  put  into  milk  to  kill  or  hinder  the  growth  of 
bacteria  by  chemical  means,  a  practice  which  is  forbidden  by  the 
pure-food  legislation  which  has  been  enacted  in  many  States.  The 
most  common  are  borax,  boric  acid,  salicylic  acid,  formalin,  and  salt- 
peter. There  are  several  decided  objections  to  their  use,  the  most 
important  being  that  they  may  seriously  injure  the  health  and  that 
they  help  to  conceal  dirt  with  the  accompanying  bacteria.  Although 
an  occasional  small  dose  may  not  be  harmful,  the  consensus  of  opin- 
ion is  that,  taken  continuously,  such  preservatives  retard  digestion 
and  have  an  irritating  efTect  on  the  intestines,  often  causing  serious 
disturbances.  They  are  of  course  most  dangerous  to  the  delicate 
organs  of  infants  and  invalids,  who  are  also  the  most  dependent  on 
milk  for  nourishment^  ^loreover,  while  they  kill  many  micro- 
(jrganisms,  they  do  not  kill  all ;   some  of  the  most  dangerous,  such  as 

71701°— Dull.  CfiC— 11 3 


18  THE   USE   OF   MILK   AS   FOOD. 

the  tubercle  bacilli,  have  been  known  to  resist  considerable  quantities. 
Finally,  they  are  so  often  emJDloyed  to  make  old  milk  pass  for  fresh, 
or  dirty  milk  for  clean,  that  their  use  in  ordinary  milk  suggests  a 
dishonest  or  a  dirty  milkman. 

CONDENSED  MILK  AND  MILK  POWDER. 

Wlien  milk  is  heated  the  water  in  it  evaporates  readily,  and  if  the 
heating  is  continued  long  enough,  as,  for  instance,  in  making  the  well- 
known  pudding  of  rice  and  milk,  cooked  slowlj^  in  the  oven  for  a  long 
time,  the  milk  becomes  thick  and  creamy.  In  the  case  of  the  pudding 
the  thickening  is  due  in  part,  of  course,  to  the  effect  on  the  starch  of 
the  rice,  but  also  in  considerable  measure  to  the  elimination  of  water 
from  the  milk.  This  fact  is  taken  advantage  of  in  the  manufacture 
of  evaporated  or  condensed  milk.  On  a  commercial  scale  the  process 
is  commonly  carried  on  in  vacuum  pans,  as  under  such  conditions  a 
lower  degree  of  heat  may  be  employed  and  the  danger  of  scorching 
is  lessened.  Sugar  is  very  commonly  added  to  condensed  milk, 
though  unsweetened  condensed  milk  is  also  a  common  commercial 
product.  Such  unsweetened  milk  evaporated  to  about  the  consist- 
ency of  cream  was  formerly  sold  under  the  name  evaporated  cream. 
Condensed  milk  is  ordinarily  marketed  in  cans  of  varying  size  and  its 
manufacture  is  an  enterprise  of  very  great  importance.  Its  low 
water  content  and  large  percentage  of  sugar  do  not  favor  bacterial 
growth,  and  so  it  will  keep  for  a  reasonable  time  after  the  cans  are 
opened.  Condensed  milk  is  used  in  many  ways  like  fresh  milk  or 
cream.  "WTien  properly  diluted  with  water  it  may  be  used  in  cookery 
like  ordinary  milk  and  is  very  satisfactory  for  the  purpose,  especially 
on  shipboard,  in  the  Tropics,  or  elsewhere  where  fresh  milk  can  not 
be  readily  obtained.  The  small  bulk  is  an  additional-  advantage  in 
shipping.  Condensed  milk  is  used  to  a  large  extent  for  infant  feed- 
ing, and  has  the  advantage  of  being  sterile,  but  it  is  not  considered 
so  satisfactory  as  fresh  milk  or  as  pasteurized  milk.  Investigations 
have  shown  that  with  children  and  adults  condensed  milk  has  prac- 
tically the  same  coefficients  of  digestibility  as  fresh  milk. 

Within  recent  years  special  devices  have  been  put  on  the  market  for 
evaporating  milk  to  a  fine  flour-like  powder,  which  is  easy  to  keep, 
nutritious,  and,  of  course,  convenient  for  shipment.  When  water  is 
added  the  resulting  mixture  closely  resembles  ordinary  milk  in  ap- 
pearance and  may  be  used  in  cookery  and  in  other  ways.  The  flavor 
depends  to  a  great  extent  upon  the  method  of  manufacture,  in  some 
cases  being  almost  the  same  as  that  of  fresh  milk,  while  in  other  cases 
a  slightly  strong  or  scorched  taste  is  present,  but  is  not  pronounced 
enough,  it  is  said,  to  be  noticeable  in  cooked  products  in  which  it 
is  used. 

363 


THE  USE   OF   MILK  AS  FOOD.  19 

The  relative  amount  of  nutrients  in  milk,  condensed  milk,  pow- 
dered, dried,  skim  milk,  and  other  milk  products,  is  shown  in  the 
table  on  page  9  and  graphically  in  the  charts  on  pages  30  and  37. 

GRADED  AND  CERTIFIED  MILK. 

There  is  so  much  difference  in  the  composition  of  milk  that  many 
large  butter  and  cheese  factories  now  test  all  the  milk  which  they 
buy  and  pay  for  it  according  to  the  amount  of  fat  which  it  contains. 
The  importance  of  such  an  arrangement  for  the  retail  millc  trade  is 
evident. 

The  terms  "  standardized  "  milk  or  "  blended  "  milk  are  applied  to 
milk  which  has  been  so  modified  as  to  contain  a  definite  amount  of 
one  or  more  of  its  constituents.  The  most  important  and  at  the  same 
time  the  most  variable  constituent  is  fat.  To  standardize  milk  as 
regards  fat  it  is  only  necessary  to  add  or  ren^ove  a  certain  amount  of 
this  constituent  or  to  add  or  remove  a  certain  amount  of  skimmed 
milk.  Directions  for  such  standardizing  or  blending  have  been  sum- 
marized in  an  earlier  publication  "  of  this  Department.  Most  States 
and  cities  now  have  a  legal  standard  for  milk,  representing  a  fair 
amount  of  fat  and  other  solids. 

If  all  milk  sold  could  be  tested  by  such  a  standard,  and  the  price 
regulated  according  as  the  milk  surpassed  or  fell  below  it,  both  pro- 
ducer and  consumer  would  be  better  satisfied,  the  producer  because 
he  would  get  credit  for  good  milk,  and  the  consumer  because  he  would 
know  what  he  was  really  buying.  Such  graded  milk  is  sold  in  some 
European  cities,  and  to  a  less  extent  in  this  country.  The  principle 
has  been  more  commonly  applied  to  cream,  of  which  different  quali- 
ties are  sold  at  prices  varying  with  the  amount  of  fat. 

In  some  of  oUr  large  cities  what  is  known  as  "  certified  "  milk  may 
be  obtained.  The  dealers'  certificate  is  usually  in  the  form  of  a  label 
pasted  over  the  top  of  the  bottle.  Under  local  pure-food  laws  the 
use  of  this  label  is  permitted  only  to  those  establishments  which  are 
periodically  inspected  by  public  officials  as  to  their  sanitarj^  condi- 
tions, and  which  market  milk  conforming  in  composition  to  a  fixed 
standard.  Such  milk  justly  commands  a  higher  price  than  that  of 
which  the  quality  is  not  thus  guaranteed. 

The  term  "  sanitary  "  milk  is  quite  commonly  used,  being  applied 
somewhat  indefinitely  to  milk  produced  and  handled  under  condi- 
tions considered  necessary  to  secure  a  pure,  wholesome  jiroduct.  It 
is  often  applied  by  dealers,  for  purposes  of  advertising,  to  milk  pro- 
duced under  decidedly  insanitary  conditions.  The  term  "  hygienic  " 
milk  is  similarly  abused. 

"  U.  S.  Dept.  Agr.,  Farmers'  Bui.  2S1. 
3G3 


20  THE   USE   OF    MILK   AS   FOOD. 

When  milk  is  passed  through  a  centrifugal  separator  much  of  the 
solid  impurities  remains  in  the  separator  slime.  A  mixture  of  the 
skim  milk  thus  purified  and  the  cream  which  was  separated  from  it 
is  often  referred  to  as  "  clarified  milk." 

CARE  OF  MILK  IN  THE  HOME. 

No  matter  liow  well  milk  has  been  handled  up  to  the  time  it  is  de- 
livered to  the  consumer,  it  can  not  be  expected  to  keep  well  if  it  is 
carelessly  treated  thereafter.  It  should  be  poured  into  pitcher,  pan, 
or  other  vessel — freshly  scalded  to  remove  any  bacteria  or  mold 
spores — and  kept  in  a  cool,  clean  place  free  from  dirt,  flies,  etc.  New 
milk  should  never  be  mixed  with  old  unless  it  is  to  be  used  at  once,  as 
the  bacteria  in  the  old  milk  w^ill  of  course  be  added  also  and  the  mixed 
milk  will  not  keep  as  well  as  the  fresh  milk  alone.  Bacteria  are  thick- 
est where  there  is  dirt  arid  decay,  and  milk  should  therefore  be  stored 
only  in  clean,  sweet  places.  It  is  safer  to  keep  it  covered,  to  exclude 
not  only  dirt  and  bacteria  but  also  the  flavors  and  odors  which  it  so 
easily  absorbs.  If  kept  at  a  temperature  of  50°  F.  or  less,  good  milk 
should  remain  sweet  for  twelve  hours,  at  least,  after  it  reaches  the 
consumer,  and  ordinarily  for  twenty-four  hours  or  more.  Sometimes 
in  very  hot  weather  housekeepers  complain  that  in  spite  of  all  pre- 
cautions it  sours  quickly,  even  in  the  ice  box.  This  is  often  due  to  the 
fact  that  the  air  of  the  ice  box,  although  it  seems  cold  in  contrast  with 
the  heat  outside,  is  really  not  cold  enough  to  check  the  growth  of  the 
bacteria  ;  if  a  thermometer  placed  inside  registers  more  than  50°  F.  the 
fault  is  almost  surely  in  the  temperature  of  the  ice  box  and  not  in  the 
milk. 

In  large  cities,  where  most  of  the  milk  comes  by  morning  trains 
from  a  considerable  distance,  it  is  often  impossible  to  deliver  fresh 
morning's  milk  in  time  for  breakfast,  and  that  milked  the  morning 
before  must  be  given  to  patrons  who  insist  on  an  early  delivery. 
They  would  get  their  milk  from  twelve  to  eighteen  hours  fresher  if 
they  would  take  it  in  the  afternoon  instead. 

DIGESTIBILITY  OF  MILK. 

The  amount  of  nourishment  which  any  kind  of  food  furnishes  to 
the  body  depends,  in  the  first  place,  on  the  food  ingredients,  the  pro- 
tein, fats,  and  carbohydrates  and  mineral  matters  which  it  contains, 
and  in  this  respect  milk  is  a  well-balanced,  nutritious  food.  But 
there  is  another  consideration  which  is  brouglit  out  l\y  the  much- 
quoted  phrase,  "  We  live  not  upon  what  we  eat  but  upon  what  we 
digest."  The  nutritive  value  of  food  depends  not  only  upon  the  ma- 
terials it  contains  but  also  upon  the  amounts  of  those  nutrients  which 

3G3 


THE  USE   OF   MILK   AS   FOOD.  21 

the  body  can  actually  utilize — upon  its  digestibility.  As  commonly 
used,  the  word  digestibility  refers  mainly  to  the  ease  and  comfort  of 
digestion.  This  is  an  important  consideration,  but  does  not  tell  the 
whole  story.  As  here  used  the  words  digestible  and  digestibility 
refer  to  the  amount  or  proportions  of  the  nutritive  ingredients  of  a 
food  material  which  may  by  the  average  healthy  digestive  organs  be 
made  available  for  the  uses  of  the  body.  Whether  milk  is  to  be 
classed  as  a  digestible  or  indigestible  food  will  therefore  depend  upon 
the  proportions  of  protein,  fats,  carbohydrates,  and  mineral  matters 
which  the  digestive  organs  of  the  average  normal  person  are  found  to 
transform  into  material  available  for  the  use  of  the  body. 

PROCESS   OF  DIGESTION. 

No  one  element  of  the  various  digestive  juices  which  act  upon  the 
food  as  it  passes  through  the  alimentary  canal  acts  upon  ail  classes  of 
nutrients.  All  are  digested  separately,  though  sometimes  simulta- 
neously. Since  milk  contains  considerable  quantities  of  each  class  of 
nutrients,  its  digestion  w^ill  be  better  understood  if  we  follow  the 
changes  in  each  nutrient  separately. 

The  protein  compounds  of  milk  are  usually  considered  to  give  the 
most  trouble  in  its  digestion,  and  this  is  mainly  due  to  the  casein. 
Milk  is  commonly  classed  as  a  liquid  food,  but  this  is  true  only  out- 
side of  the  body;  as  soon  as  it  reaches  the  stomach  the  rennin  of 
the  gastric  juice  precipitates  the  casein  into  a  curd  from  which  the 
other  ingTedients  are  separated,  much  as  the  whey  separates  from 
the  curd  in  cheese  making.  Sometimes  the  curd  tends  to  become 
tough  and  leathery  and  consequently  difficult  for  the  digestive  juices 
to  work  upon.  This  is  especially  marked  when  for  any  reason  there 
is  considerable  calcium  phosphate  present,  and  may  be  partially 
prevented  by  adding  limewater  to  the  milk.  The  acid  and  the  pepsin 
of  the  gastric  juice  together  work  upon  the  curd  and  render  a  small 
part  of  it  more  soluble,  but  the  bulk  of  the  casein  is  digested  in  the 
small  intestine  by  the  trypsin  of  the  pancreatic  juice.  Experiments  <* 
have  shown  that  casein  which  has  not  been  curdled  b}'^  rennin  is  more 
completely  digested  by  trypsin  than  the  curdled.  Apparently,  then, 
the  formation  of  the  curd,  especially  when  tough  and  leathery,  means 
extra  work  for  the  digestive  organs. 

The  albumin  of  the  milk  is  for  the  most  part  easily  digested  by 
either  the  pepsin  or  the  trypsin. 

The  digestion  of  fats  depends  mainly  upon  getting  the  globules 
into  such  fine  size  that  they  may  be  easily  passed  through  the  walls 
of  the  intestines.    Separating  the  fat  into  such  tiny  globules  is  called 

"Arch.  Physiol.  [Pfliiger]    (1902),  p.  G05. 
363 


22  THE   USE   OF    MILK   AS   FOOD. 

emulsification.  Another  change,  saponification,  also  helps  in  the 
absorption  of  fat.  The  alkaline  pancreatic  juice  unites  with  the  fatty 
acids  of  the  fat  to  form  a  soap,  while  the  glycerin  is  set  free,  much 
as  in  ordinary  soap  making.  Both  the  soap  and  the  glycerin  are 
more  easily  absorbed  than  the  original  fat.  The  fat  globules  of  milk 
are  smaller  than  those  from  most  other  foods  and  are  more  easily 
emulsified;  for  this  reason  milk  fat  is  commonly  thought  to  be  the 
most  easily  and  thoroughly  digested  of  the  fats  in  the  ordinary  diet. 
As  has  been  said,  the  size  of  the  globules  varies  in  milk  from  dif- 
ferent animals.  There  is  a  theory  that  the  fat  of  milk  containing 
the  larger  globules — that  is,  milk  on  which  cream  rises  freely  (see 
p.  13) — is  less  easily  digestible  than  that  in  which  smaller  globules 
remain  longer  in  suspension. 

Ordinarily  the  digestion  of  carbohydrates  is  begun  by  the  saliva 
in  the  mouth,  and  ceases  in  the  stomach  after  the  food  is  swallowed, 
owing  to  the  acid  reaction  of  the  gastric  juice.  The  results  of  recent 
investigations  make  it  seem  certain  that  usually  the  digestion  of 
carbohydrates  continues  in  the  stomach  for  a  much  longer  period 
than  was  formerly  supposed.  Milk  is  so  quickly  swallowed  that  the 
saliva  would  have  little  chance  to  act  upon  the  milk  sugar  in  the 
mouth.  Just  how  far  this  digestion  would  continue  in  the  stomach 
before  being  checked  by  the  gastric  juice  it  is  impossible  to  say,  but 
there  is  every  reason  to  suppose  that  under  usual  and  normal  con- 
ditions the  bulk  of  the  milk  sugar  is  digested  by  one  of  the  ferments 
of  the  pancreatic  juice  after  it  passes  from  the  stomach  into  the 
intestines.  Eecent  French  studies"  indicate  that  the  major  portion 
of  milk  and  milk  products  leave  the  stomach  within  an  hour  and  a 
half.  It  is  commonly  supposed  that  the  lactic  acid  of  sour  milk  is 
changed  to  simpler  bodies  in  the  digestive  tract  and  assimilated,  and 
its  presence  may  even  be  beneficial  in  checking  the  growth  of  the 
putrefactive  bacteria  that  cause  intestinal  disorders.     (See  p.  41.) 

PROPORTION    OF    NUTRIENTS    DIGESTED. 

In  connection  with  the  nutrition  investigations  of  the  Office  of 
Experiment  Stations  many  experiments  have  been  made  to  determine 
how  thoroughly  the  protein,  fats,  and  carbohydrates  of  milk  are 
digested  and  assimilated,  and  much  similar  work  has  been  reported 
by  other  investigators.  The  results  obtained  vary  within  rather  wide 
limits,  owing  either  to  individual  peculiarities  of  the  subject  or  to 
conditions  under  which  the  milk  was  taken. 

In  persons  who  digest  milk  well  the  average  coefficients  of  digesti- 
bility may  run  as  high  as  98  per  cent  for  protein,  99  per  cent  for  fat, 
and  99  per  cent  for  carbohydrates.     The  average  values  for  animal 

<^Rev.  G6n.  Lait,  6  (1907),  p.  441. 
363 


THE   USE   OF    MILK    AS   FOOD.  23 

food  are  97  per  cent  protein,  95  per  cent  fat,  and  98  per  cent  carbo- 
hydrates. In  general  it  seems  fair  to  say  that  milk  is  on  an  average 
as  well  or  even  more  thoroughly  digested  than  other  animal  foods. 
When  milk  is  the  only  food  eaten  by  healthy  adults  considerably  less 
of  the  nutrients  supplied  are  assimilated  than  is  the  case  when  it 
forms  a  part  of  a  mixed  diet,  doubtless  owing  to  the  fact  that  the 
casein  is  apt  to  coagulate  in  the  stomach  into  large  lumps  which 
resist  the  action  of  the  digestive  juices.  It  has  been  shown  by  experi- 
ments that  when  finer  coagulation  is  secured  the  thoroughness  of  the 
digestion  is  increased.  Taking  other  food  with  the  milk  hinders  the 
formation  of  the  lumps  of  casein  in  the  stomach  and  so  increases  the 
thoroughness  of  digestion  of  milk.  Of  course,  very  young  children 
digest  mothers'  milk  alone  better  than  any  other  food,  but  this  is 
because  of  the  peculiarities  of  their  digestive  organs,  to  which  such 
milk  is  thoroughly  adapted  by  nature,  both  in  composition  and  in 
physical  properties.  If  other  milk  is  substituted  for  mother's  milk 
it  must  be  modified  to  secure  best  results.  For  adults  in  poor  health 
milk  is  very  commonly  a  most  important  food,  and  many  individuals 
whose  digestive  organs  are  not  in  good  condition  can  derive  more 
benefit  from  a  milk  diet  than  from  any  other  single  food, 

RELATIVE  VALUE  OF  COOKED  AND  RAW  MILK. 

As  was  stated  in  an  earlier  section  (p.  16),  the  heat  of  cooking  pro- 
duces certain  chemical  changes  which  alter  the  flavor  and  appearance 
of  milk.  In  how  far  these  changes  affect  its  digestibility  is  a  point 
on  which  authorities  differ  greatly,  for  although  many  experiments 
have  been  made  to  determine  the  facts  of  the  case,  the  results  are 
very  conflicting.  The  principal  changes,  apart  from  the  destruction 
of  more  or  less  of  the  bacteria,  are  as  follows :  Part  of  the  protein  is 
coagulated,  it  is  believed,  and  the  protein  undergoes  cleavage  to  some 
extent — that  is,  the  molecule  is  split  up  into  simpler  forms,  one  of 
which  is  a  volatile  sulphur  compound  which  gives  freshly  boiled  milk 
its  peculiar  odor.  If  the  milk  is  cooked  in  an  open  vessel  the  forma- 
tion of  more  or  less  of  a  film  or  "  skin  "  accompanies  the  other 
changes,  though  it  is  interesting  to  note  that  the  formation  of  this 
skin  and  some  of  the  disagreeable  features  which  accompany  it  may 
be  more  or  less  prevented  by  stirring  the  milk  while  it  is  heating. 
The  character  of  the  fat  globules  appears  to  be  somewhat  altered  by 
cooking,  although  the  nature  of  the  changes  is  not  yet  thoroughly 
understood;  some  of  the  other  compounds  which  occur  in  small 
quantities  also  undergo  cleavage  and  give  place  to  new  ones.  The 
carbohydrates  undergo  practically  no  change  unless  the  heat  is  con- 
tinued long  enough  to  caramelize  some  of  the  milk  sugar.  The 
longer  or  harder  the  cooking,  the  more  noticeable  are  the  changes. 

363 


24  THE   USE   OF   MILK   AS  FOOD. 

The  skin  formed  by  heating  has  been  commonly  said  to  consist 
largel}^  of  coagulated  albumin,  but  later  investigators  having  found 
casein  and  lime  salts  in  it  have  suggested  that  the  heat,  possibly  by 
driving  off  carbon  dioxid,  liberates  casein  from  lime  salts,  by  which 
it  is  supposed  to  be  held  in  solution,  which  then  rises  to  the  surface 
and  is  more  or  less  dried  by  rapid  surface  evaporation.  If  the  skin 
is  removed  it  will  form  again,  and  apparently  will  continue  to  do  so 
indefinite!}'.  That  the  amount  of  material  which  may  be  thus  re- 
moved is  not  great  is  indicated  by  tests  °  in  which  the  skin  from 
100  cubic  centimeters  of  milk  boiled  for  a  quarter  of  an  hour  did 
not  contain  more  than  0.27  gram  of  protein. 

The  question  has  been  studied  more  recently  by  Jamison  and  Hertz,^ 
whose  experiments  showed  that  the  formation  of  skin  or  film  on 
milk  is  not  a  peculiar  propertj?^  of  lactalbumin  or  of  casein,  since  a 
similar  film  may  be  produced  bj^  warming  any  protein  solution  which 
contains  emulsified  fat.  Drying  was  found  to  be  an  essential  con- 
dition for  such  skin  formation.  The  character  of  the  films  formed 
on  milk  and  other  protein  solutions  was  studied,  and  the  conclusion 
drawn  that  the  film  is  probably  composed  of  dried  protein  with  fat 
entangled  in  it. 

This  coagulation  of  the  protein  compounds  roughly  resembles  the 
hardening  of  the  white  of  eggs  in  boiling,  which  is  commonly  said  to 
render  the  egg  albumin  less  easy  of  digestion.  Doubtless  for  this 
reason  it  has  been  supposed  that  boiled  milk  is  less  easily  digested 
than  raw  milk.  Boiled  milk  coagulates  less  rapidly  than  raw  milk, 
but  under  the  influence  of  rennin  the  casein  of  the  former  forms  about 
as  tough  a  curd  as  that  of  the  latter.  In  some  processes  of  cheese 
making  milk  is  heated  before  it  is  curdled. 

It  may  be  that  cooked  milk  fat  is  less  easily  emulsified  than  raw, 
but  not  enough  is  known  to  say  definitely,  and  the  difference,  if  it 
exists,  is  probably  slight. 

Many  physicians  consider  that  infants  fed  for  a  long  time  on  boiled 
or  sterilized  milk  show  a  greater  tendency  to  scurvy,  rickets,  and  other 
diseases  of  malnutrition  than  when  raw  or  pasteurized  milk  is  used. 
No  satisfactory  explanation  for  this  has  yet  been  given,  but  there 
seems  some  reason  for  believing  that  it  has  to  do  with  changes  in- 
duced in  the  character  of  the  calcium  salts  present. 

Probably  much  of  the  difference  of  opinion  regarding  the  value 
of  boiled  milk  is  due  to  individual  peculiarities.  Some  healthy  per- 
sons who  can  not  eat  raw  milk  with  comfort  have  no  trouble  with  it 
boiled,  while  others  whom  the  taste  of  boiled  milk  sickens  are  very 
fond  of  it  raw.     Foods  whoso  taste  offends  the  palate  do  not  stimu- 

ttArcb.  Hyp.,  2S  (1897),  p.  43. 
''Jour.  Physiol.   [Loudou],  27    (1901-2),  p.  2G. 
363 


THE   USE    OF    MILK   AS   FOOD.  25 

late  the  flow  of  digestive  juices  as  do  pleasant  ones,  and  so  it  doubt- 
less would  be  wisest  for  the  ordinary  healthy  person  to  consult  his 
taste  in  choosing-  between  the  raw  and  cooked  milk.  As  for  infant 
feeding,  when  artificial  feeding  is  necessary,  probably  the  majority 
of  physicians  recommend  raw  or  pasteurized  milk  vmless  the  Aveather 
is  very  hot,  or  the  quality  of  the  milk  very  suspicious,  or  unless  it  is 
necessary  to  keej)  the  milk  a  long  time,  as  in  traveling.  It  goes  with- 
out saying  that  in  infant  feeding  the  use  of  cow's  milk  should  always 
presuppose  a  product  as  free  as  possible  from  bacterial  contamination. 

MILK  FOR  INFANTS— MODIFIED  MILK— HOMOGENIZED  MILK. 

It  is  universally  admitted  that  the  best  food  for  infants  is  milk 
from  strong,  healthy  women.  When  this  is  not  obtainable  the  more 
nearly  the  substitute  resembles  it  the  better.  The  milk  of  the  ass  and 
the  mare  are  in  many  important  respects  more  like  human  milk  than 
is  that  of  the  cow,  and  their  milk  used  frequently  to  be  given  to 
babies.  Goat's  milk,  too,  is  highly  thought  of  under  ordinary  cir- 
cumstances. At  present,  however,  cow's  milk  is  the  most  common 
substitute,  and  when  necessary  this  is  artificially  modified  to  make  it 
resemble  human  milk  more  closely. 

A  glance  at  the  table  on  page  8  shows  that  while  cow's  milk  con- 
tains about  the  same  proportion  of  total  solids  and  fat  as  woman's 
milk  it  carries  more  protein  and  less  milk  sugar.  Besides  this  it 
has  larger  fat  globules  and  there  is  more  casein  in  proportion  to  the 
albumin  and  the  casein  is  said  to  form  a  tougher  curd  than  that  of 
human  milk.  The  deficiency  in  milk  sugar  in  the  cow's  milk  can 
easih'^  be  made  good  by  adding  either  milk  sugar  itself  or  some  other 
digestible  carbohj'drate,  such  as  rice  flour  or  arrowroot.  The  casein 
may  be  made  more  easy  of  digestion  by  the  addition  of  limewater, 
or  may  be  artificially  predigested  by  peptonizing.  But  nothing  can 
exactly  reproduce  the  protein  of  human  milk,  and  for  this  reason, 
perhaps  more  than  for  any  other,  cow's  milk,  no  matter  how  skill- 
fully modified,  is  never  quite  so  satisfactory  as  human  milk  for 
infants. 

Fortunately,  most  healthy  babies  thrive  on  good  cow's  milk  or 
cow's  milk  simply  modified.  It  is  the  sickly  who  recj[uire  special 
preparations,  and  their  needs  vary  so  greatly  that  only  the  physician 
acquainted  with  the  case,  and  not  always  he,  can  say  what  change  is 
necessary. 

Eecognizing  the  important  bearing  of  the  size  of  the  globules  of 
the  milk  fat  upon  digestion,  so-called  homogenized  milk  is  now  pre- 
pared, though  it  is  not  so  well  known  or  so  generally  used  as  modi- 
fied milk.  In  such  milk  the  fat  globules  are  broken  down  by 
mechanical  means  into  very  fine  particles  which  show  no  marked 

3C3 


26  THE   USE   OF    MILK   AS   FOOD. 

tendency  to  rise  to  the  surface  as  do. the  fat  globules  of  ordinary  size. 
This  change  in  the  fat  globules  is  usually  accomplished  by  forcing 
the  milk  through  capillar}'  tubes  and  against  a  resisting  surface. 
The  force  of  impact  causes  the  breaking  up  of  the  globules  and  thus 
makes  a  more  perfect  emulsion  of  the  milk. 

SPECIAL  INFANT  FOODS. 

There  are  numerous  patent  infant  and  invalid  foods  on  the  market, 
some  of  which  contain  cow's  milk  as  a  basis  combined  with  varying 
amounts  of  carbohydrates  or  other  constituents,  and  others  which 
seem  to  be  made  of  farinaceous  materials  without  milk.  In  some 
cases  the  carbohydrates  have  apparently  been  malted  l)efore  being 
combined  with  milk  or  else  malt  extract  is  added  during  the  process 
of  manufacture. 

The  jDcrcentage  composition  of  the  two  types  of  infant  foods  is 
shown  in  the  table  on  page  9.  The  chart  on  page  37  shows  in 
graphic  form  how  commercial  infant  food,  such  as  is  sold  in  dry 
form,  in  bottles,  or  in  cans,  and  is  made  of  milk  and  starch,  compares 
with  some  other  milk  products.  It  is  also  interesting  to  compare 
this  product  with  the  data  showing  the  composition  of  whole  milk, 
skim  milk,  etc.,  included  in  Chart  II,  p.  30. 

Experience  has  shown  that  these  special  milk  foods  (when  they 
really  contain  the  nutrients  of  milk)  are  useful  and  valuable  for 
infants  where  it  is  necessary  to  resort  to  some  method  of  artificial 
feeding,  but  every  one  recognizes  that  where  possible  mother's  milk 
is  the  best  food  for  the  young  child.  Too  much  credence  should  not 
be  given  to  the  extravagant  claims  made  for  some  brands  of  infant 
foods.  The  safest  course  is  undoubtedly  to  follow  the  advice  of  a 
competent  physician  in  selecting  the  substitute  for  natural  feeding. 
It  is  often  wiser  to  use  modified  cow's  milk  in  preference  to  these 
commercial  foods,  and  it  can  be  easily  prepared  at  home  imder  a 
physician's  directions.  There  are  also  milk  laboratories  in  many  of 
our  large  cities  and  towns  where  modified  milk  of  all  sorts  can  be. 
procured  on  prescription. 

All  babies  fed  on  raw  cow's  milk  are  in  more  or  less  danger  from  the 
undesirable  bacteria  which  it  may  contain  and  which  cause  diarrhea 
and  other  serious  infant  disorders.  The  question  of  pasteurizing  and 
sterilizing  milk  in  order  to  avoid  this  danger  has  already  been  spoken 
of  (p.  16).  When  raw  milk  is  used,  great  pains  should  bo  taken  not 
only  to  obtain  fresh,  clean  milk,  but  also  in  caring  for  it  scrupulously 
after  it  is  purchased.  It  is  usually  more  important  that  the  milk 
should  be  i:)ure  than  that  it  shoidd  be  rich  in  cream,  especially  as  the 
fat  in  very  creamy  milk  may  be  less  digestible  on  account  of  the  size 
of  the  fat  globules. 

3G3 


THE   USE   OF    MILK   AS   FOOD, 


27 


NUTRITIVE  VALUE  OF  MILK  COMPARED  WITH  OTHER  FOODS. 

The  value  of  milk  for  noiirisliment  is  not  as  generally  understood  as 
it  should  be.  Many  people  think  of  it,  for  adults  at  least,  as  a  bever- 
age rather  than  a  food,  and  do  not  realize  that  a  glass  of  it  adds  as 
much  to  the  nutritive  value  of  a  meal  as  a  quarter  of  a  loaf  of  bread 
or  a  good  slice  of  beef.  A  quart  of  average  milk  contains  the  same 
amount  of  nutritive  ingredients  as  0.75  of  a  pound  of  beef  or  6  ounces 
of  bread.  To  put  it  in  another  way,  about  one-eighth  of  the  whole 
weight  of  the  milk,  one-third  of  the  beef,  and  two-thirds  of  the  bread 
consist  of  actually  nutritive  ingi'edients.  The  other  seven-eighths  of 
the  milk  and  one-third  of  the  bread  are  water,  while  the  two-thirds  of 
the  meat  which  is  not  actual  nutriment  is  mainly  water,  though  in 
part  is  bone.  Chart  I  shows  the  average  composition  of  milk,  milk 
products,  and  some  other  common  food  materials.  In  this  chart  the 
percentage  amount  of  refuse,  water,  protein,  fat,  carbohydrates,  and 
mineral  matter  or  ash.  is  indicated  by  shaded  portions  corresponding 
to  these  different  constituents,  each  full  division'  of  the  lines  repre- 
senting constituents  being  equivalent  to  10  per  cent.  The  heavy 
black  line  indicates  the  number  of  calories  per  pound,  each  full 
division  of  this  space  corresponding  to  400  calories. 

As  compared  with  the  animal  foods,  it  Avill  be  noted  from  this 
chart  that  milk  contains  more  carbohydrates  and  has  no  refuse.  In 
these  two  resj^ects  it  resembles  more  nearly  many  of  the  vegetable 
foods,  such  as  flour,  oatrheal,  and  the  like.  The  amount  of  mineral 
matter  is  much  the  same  as  in  the  other  fresh  substances  given. 
There  is  a  larger  proportion  of  water  in  milk  than  in  most  other 
food  materials  except  very  succulent  fruits  and  vegetables,  so  that  a 
given  weight  contains  less  dry  matter  or  nutrients  than  most  foods. 

If  we  wish  to  compare  the  food  values  of  the  actually  nutritive 
ingredients  (the  dry  matter  contained  in  the  edible  portion)  of  dif- 
ferent food  materials,  the  calculations  may  be  made  on  the  basis  of 
1  pound  of  this  water- free  edible  portion,  and  the  following  figtires 
show  such  a  comparison  of  milk  and  a  few  other  foods : 

Nutrients  and  energy  in  1  pound  of  the  water-free  edible  portion  of  several 

food  materials. 


Food  materials. 


Protein. 

Fat. 

Carbohy- 
drates. 

Mineral 
matter. 

Pound. 

Pound. 

Pound. 

Pound. 

0.25 

0.31 

0.39 

0.05 

.36 

.03 

.56 

.06 

.33 

.06 

.53 

.08 

.39 

.52 

.03 

.06 

.57 
.26 
.13 

.40 
.06 
.01 

.03 
.08 
.01 

.85 

.15 

.02 

.82 

.01 

.10 

.01 

.85 

.01 

.03 

.03 

.92 

.02 

Fnel 
value. 


Whole  milk 

Skim  milk  (0.3  per  cent  fat) 

Buttermilk 

Cheese 

Beef,  round 

Smoked  ham , 

Wheat  flour 

Wheat  bread , 

Potatoes , 

Apples 

363 


Calorics. 
2,475 
1,835 
LS-IS 
2,990 
2,750 
3,275 
1,8C5 
1,865 
1,790, 
1,885 


28 


THE   USE   OF    MILK   AS   FOOD. 


Chart  I. — Percentage  composition  and  fuel  value  of  milk,  milk  products,  and 

some  other  foods. 

(The  constituents  are  expressed  in  per  cent,  the  fuel  values  In  calories  per  pound.) 


Protein.      Tats.       Carbo-    IJinoral 
hydrates,  mailers. 


Water.     Refuse. 


Fuel  value. 


Oysters 


Corn  meal 


Oatmeal- 


Beans,  di'ied 


Potatoes- 


M:^mmMmmmmmmmmmmmmmmmmm. 


Sugar- 


3G3 


THE   USE    OF    MILK    AS   FOOD.  29 

One  of  the  most  common  statements  regarding  milk  is  that  it  is  a 
"  perfect  food."  In  one  sense  this  is  true,  but  in  another  it  is  not. 
The  normal  milk  of  any  mammal  may  be  perfectly  adapted  to  the 
nourishment  of  its  offspring,  but  the  milk  of  one  mammal,  such  as 
the  cow,  is  not  necessarily  a  perfect  food  for  the  young  of  another 
species,  such  as  the  human  infant;  nor  is  any  milk  a  perfect  food  for 
a  healthy  adult  of  any  species.  Though  an  extrehiely  valuable  food, 
difl'ering  from  all  others  except  possibly  eggs  in  that  it  contains 
fairly  good  proportions  of  all  the  ingredients  necessary  for  the  build- 
ing and  repair  of  the  body  and  for  supplying  it  with  energ}'  for  its 
activities,  the  ingredients  are  so  diluted  with  water  that  it  would 
require  a  large  quantity  (4  or  5  quarts  each  day)  to  meet  the  needs 
of  the  adult  body,  and  to  get  the  required  amount  of  energy  from 
milk  unnecessary  quantities  of  protein  must  be  consumed.  Further- 
more, healthy  digestive  organs  can  do  their  work  better  when  at  least 
part  of  the  food  is  in  solid  form.  Even  for  adults,  however,  milk 
alone  can  support  life  for  a  considerable  time,  if  not  indefinitely,  but 
its  chief  value  is  in  combination  with  other  foods;  not  as  a  beverage 
merely,  but  to  supply  in  part  the  material  needed  for  the  body.  For 
infants  it  is  almost  indispensable,  and  for  invalids  it  is  a  nutritious, 
easily  digested  food,  Avhich  the  physician  can  readily  control. 

NUTRITIVE   VALUE   OF   SKIM   MILK. 

As  every  one  knows,  skim  milk  is  the  milk  which  remains  after  the 
butter  fat — that  is,  cream — has  been  removed.  In  the  ordinary  proc- 1 
ess  of  skimming  the  cream  is  allowed  to  rise  in  pans  or  other  conven- 
ient receptacles,  and  the  la^'er  of  cream  on  top  is  removed  with  a 
skimmer  or  some  other  convenient  device.  Formerly  hand  skimming 
was  universal,  but  at  the  present  time  milk  separators  are  in  common 
use,  which  embody  in  their  construction  the  physical  principle  that 
with  rapidly  rotating  material  the  heavier  body  moves  from  the  cen- 
ter to  the  circumference  more  rapidl}'  than  the  lighter  body.  Milk 
separators  permit  of  the  convenient  removal  of  any  desired  propor- 
tion of  the  butter  fat,  and  in  general  remove  the  fat  much  more  com- 
pletely than  is  possible  by  hand  skimming. 

In  Chart  II  (see  p.  30)  the  outline  figure,  representing  the  glass  of 
milk  or  some  other  convenient  quantity,  is  so  divided  that  the  per- 
centage an.iount  of  the  different  constituents  is  indicated  graphically. 
In  the  case  of  fuel  values,  the  rectangular  figure,  representing  1,000 
calc>ries  or  some  multiple  of  1,000,  is  so  divided  thai  the  black  portion 
indicates  the  number  of  calories  per  pound  supplied  b}^  the  food 
material  under  consideration. 

When  whole  milk  and  skim  milk  are  compared,  as  in  the  table  on 
page  9,  and  the  chart  on  page  30,  it  will  be  seen  that  though  the  latter 

363 


30 


THE   USE    OF    MILK   AS   FOOD. 


is  deficient  in  fat  this  is  not  the  case  as  regards  protein,  carbohydrates, 
and  ash.  This  is  even  more  evident  when  tlie  two  sorts  of  milk  are 
compared  on  a  dry-matter  basis.  Such  a  comparison  suggests  a  very 
important  topic,  namely,  the  great  nutritive  value  of  skim  milk. 
Even  after  average  milk  is  skimmed — that  is,  after  the  bulk  of  the 
fat  is  removed — the  solids,  or  nutritive  ingredients,  still  make  up 
nearly  one-tenth  of  its  entire  weight.  The  amount  of  fat  left  in  skim 
milk  varies  greatly  with  the  method  of  creaming.     Ordinary  open. 


Chart  II. — Percentage  composition  and  fuel  value  per  pound  of  whole  milk  and 

some  milk  products, 

(The  constituents  are  expressed  in  per  cent,  the  fuel  values  in  calories  per  pound.) 


W/^Ol£  M/IH 


S/(/M  M/LK 


P/fors/A/:  3.3 
■c^RBOHYOM/tres  :5.  o 


^OT£-/A/ :  3.4- 


rU£l   VALU£: 


UNSWEETENED 
CONDENSED  MILK 


3IO  C/ILOM/HS  PSTR  POUND 


FUEL   VALUC: 


f6S  C4LOP/SS  P£^  POUNO. 


BUTTERMILK 


FAT.a 


/iSH:l.7 


780  CALOPiES  P£f( POUND 


pp6re//v:3.o 

-C/^/fBOHYOPATSS.'^.a 


ppor£//v:2.S 

<:/l/^BOf/yDP/tTSS:4:  S 


FUEL  VALUE: 


Pt/SL  value: 


/60  CALORIES  PER  POUND 


86S  CALOR/ES  PER  POUND 


shallow  pan  setting  leaves  anywhere  from  one-tenth  to  one- fourth  of 
the  original  fat  of  the  milk  in  the  skim  milk.  Deep,  cold  setting 
removes  the  fat  much  more  completely,  and  separator  skim  milk  has 
usually  less  fat  than  that  from  deep,  cold  setting.  It  is  not  far  out 
of  the  way,  however,  to  say  that  a  pound  of  skim  milk  contains  on  the 
average  0.034  pound  protein  and  has  a  fuel  value  of  170  calories,  or 
a  little  greater  proportion  of  protein  than  the  same  weight  of  whole 
milk  and  about  one-half  the  fuel  value. 


363 


THE   USE    OF   MILK    AS   FOOD. 


31 


In  the  ordinary  mixed  diet  a  sufficient  amount  of  fat  is  supplied  by 
meat,  butter,  lard,  etc.,  so  that  the  loss  of  this  ingredient  is  of  rela- 
tively little  importance.  Protein,  on  the  other  hand,  is  the  most 
costly  of  the  food  ingredients  and  the  one  most  likely  to  be  lacking  in 
inexpensive  meals,  and  this  is  the  nutrient  which  skim  milk  supplies 
in  a  cheap  and  useful  form.  The  value  of  skim  milk  as  food  is  not 
generally  appreciated.  Taken  by  itself  it  is  rather  "  thin  "  and,  to 
use  a  common  expression,  "  does  not  stay  by."  It  is  not  as  rich  in 
flavor  as  Avhole  milk,  but  when  taken  with  bread  or  used  in  cooking, 
it  forms  a  very  nutritious  addition  to  the  food.  A  j^ound  of  lean 
beef  (round  steak,  for  example)  contains  about  0.18  pound  of  pro- 
tein and  has  a  fuel  value  of  870  calories.  Two  and  a  half  quarts  or 
5  pounds  of  skim  milk  will  furnish  nearly  the  same  amount  of  protein 
and  have  about  the  same  fuel  value  as  the  pound  of  round  steak, 
while  it  would  cost  hardly  a  quarter  as  much.  Two  quarts  of  skim 
milk  have  a  greater  nutritive  value  than  a  quart  of  oysters ;  the  skim 
milk  has  0.14  pound  of  protein  and  a  fuel  value  of  680  calories,  while 
the  oj^sters  contain  only  0.12  pound  of  protein  and  have  a  fuel  value 
of  470  calories.  The  nutriment  in  the  form  of  oysters  would  cost 
from  30  to  50  cents,  while  the  2  quarts  of  skim  milk  Avould  liave  a 
market  value  of  from  4  to  6  cents  and  a  value  on  the  farm  of  from 
2  to  4  cents. 

A  lunch  or  meal  of  bread  and  skim  milk  is  very  nutritious  in  pro- 
portion to  its  cost  and  convenience,  as  the  following  computation 
shows : 

Composition  and  cost  of  a  lunch  or  meal  of  bread  and  skim  milk. 


Food  materials. 

Amount. 

Estimated 
cost. 

Protein. 

Fuel 
value. 

Bread 

Ounces. 
8 
8 

Cents. 

3 
2 

Pound. 

0.05 

.04 

Calories. 
601 

255 

Total 

5 

.09 

859 

The  commonly  accepted  standard  for  a  man  at  moderately  active 
muscular  work  calls  for  0.28  pound  of  protein  and  a  fuel  value  of 
3,500  calories  per  day,  so  that  the  above  lunch  furnishes  very  nearly 
one-third  of  a  day's  nutriment  and  at  a  cost  of  but  5  cents.  If  whole 
milk  were  used  instead  of  skim  milk,  the  cost  would  be  about  7  cents 
and  the  fuel  value  1,080  calories,  while  the  protein  would  remain  the 
same  in  amount. 

363 


32 


THE   USE   OF   MILK  AS   FOOD, 


The  following  lunch,  such  as  might  be  obtained  in  a  restaurant  or 
lunch  room,  will  serve  for  the  purpose  of  comparison : 

Estimated  cost  and  nutrients  of  a  restaurant  lunch. 


Food  materials. 

.\mount. 

Estimated 
cost. 

Protein. 

Fuel 
value. 

Soup 

Ounces. 
8.0 
2.0 
2.0 
1.0 
3.0 
.5 

1.0 
.5 

Ctnls. 

Pound. 

0.01 

.02 

Calorics. 
75 

Beet 

275 

100 

15 

Bread 

.02 

225 

Butter                    

100 

Coffee: 

Milk 

20 

65 

Total  

15-20 

.03 

865 

It  will  thus  be  seen  that  the  15-cent  lunch,  containing  nine  different 
food  materials,  would  not  have  any  greater  nutritive  value  than  the 
6-cent  lunch  of  bread  and  skim  milk;  though  it  contained  a  few 
calories  more  of  energy,  it  w-ould  yield  only  about  half  as  much 
protein. 

The  idea  that  only  whole  milk  is  fit  to  use,  which  is  rather  errone- 
ously held  by  housewives,  is  perhaps  ascribable  to  the  esteem  in 
which  cream  is  held  as  an  ingredient  of  "  rich  food,"  and  may  lead 
to  quite  needless  waste  or  expenditure.  For  growing  children,  who 
need  large  quantities  of  j)rotein  and  carbohydrates,  2  quarts  of  skim 
milk  would  supply  more  of  these  constituents  and  more  ash  than  1 
quart  of  whole  milk,  and  it  has  alread}'^  been  suggested  that  fresh 
skim  milk  of  good  qualit}^,  sold  under  its  real  name  and  at  a  reasonable 
price,  is  preferable  to  suspicious  whole  milk.  Many  families  who 
are  in  the  habit  of  drinking  whole  milk  and  buying  cream  would 
doubtless  be  quite  as  Avell  off  if  the  top  of  the  milk,  say  2  or  3  inches 
in  a  quart  bottle,  were  poured  into  the  cream  instead  of  the  milk 
pitcher;  the  milk  ought  still  to  be  far  from  thin  and  blue,  and  there 
would  be  a  marked  saving  in  the  cost  of  cream.  On  the  farm  skim 
milk  is  often  considered  fit  only  for  the  pigs;  but  it  really  may  be 
used  in  cookery,  etc.,  as  a  useful  and  economical  food,  though  it  is 
only  fair  to  say  that  on  a  farm  milk  is  often  so  abundant  that  the 
fresh  whole  milk  will  naturally  be  selected  for  culinary  and  table 
purposes.  The  fresh  whole  milk  seems  to  most  persons  more  tempt- 
ing as  a  beverage,  perhaps,  than  older  skim  milk,  though  this  is  a 
matter  largely  of  cultivation  and  habit;  but  if  no  one  cares  to  drink 
it  the  skim  milk  can  always  be  used  in  cooking,  as  will  be  discussed 
in  a  later  section,  a  fact  of  more  importance  from  the  standpoint  of 
economy  in  families  where  milk  is  purchased  than  in  those  where  it 
is  produced. 

3G3 


THE  USE  OF  MILK  AS  FOOD.  33 

COST  OF  NirTRIENTS  IN  WHOLE  MILK  AND  SKIM  MILK. 

Just  as  the  nutritive  value  of  a  given  food  depends  not  simply  on 
its  chemical  composition  but  on  its  proportion  of  digestible  nutrients, 
so  its  real  cheapness  or  dearness  depends  not  on  the  price  per  quart 
or  per  pound,  but  on  the  amount  of  digestible  nutrients  which  a  given 
sum  will  jiurchase.  Milk  is  economical  in  the  sense  that  it  contains 
no  refuse,  such  as  the  bone  and  gristle  of  meat,  the  shells  of  eggs, 
and  the  skins  and  seeds  of  vegetables.  Moreover,  the  proportion  of 
its  nutrients  which  can  be  digested  and  utilized  by  the  body  is,  under 
ordinary  circumstances,  larger  than  that  from  most  food  materials. 
The  thing  which  might  make  milk  expensive  is  its  diluteness — that 
is,  the  large  amount  of  water  which  it  contains  in  proportion  to  its 
solid  matter. 

The  accompanying  chart  will  help  in  showing  the  real  cheapness 
or  dearness  of  milk  at  various  prices  as  compared  with  other  foods. 
In  this  chart  the  amount  of  nutrients  is  indicated  by  the  shaded 
portions  corresponding  to  the  protein,  fat,  and  carbohydrates,  the 
length  of  each  portion  representing  the  number  of  pounds  or  frac- 
tions of  a  pound  of  the  constituent  which  is  supplied,  each  full 
division  of  the  chart  being  equivalent  to  1  pound.  The  heavy  black 
line  indicates  the  number  of  calories  per  pound,  each  full  division 
of  the  chart  corresponding  to  2.000  calories. 

The  whole  milk  represented  contains  the  average  am.ounts  of  solid 
matter,  regardless  of  price.  Milk  selling  at  10  cents  a  quart  ought 
to  contain  larger  proportions  than  that  selling  at  5  or  6,  besides 
having  fewer  bacteria;  on  the  other  hand,  milk  at  the  lower  prices 
may  occasionally  contain  larger  proportions  than  the  more  expensive, 
but  it  is  impossible  to  represent  such  variations  satisfactorily.  For 
the  purposes  of  the  present  comparison  the  average  composition  will 
be  sufficiently  accurate. 

Of  course,  in  comparing  milk  and  such  material  as  dried  beans, 
one  must  take  into  account  the  fact  that  the  beans  will  absorb  con- 
siderable water  in  cooking  and  that  a  pound  of  them  ready  to  eat 
would  not  contain  as  much  nourishment  as  is  represented  in  the  chart, 
while  milk  is  consumed  as  bought.  In  addition,  the  cost  of  cooking 
must  always  be  considered  in  connection  with  foods  which  are  not 
eaten  raw. 

Bearing  these  things  in  mind,  we  see  that  milk  at  all  but  the  highest 
prices  assumed  is  a  cheaper  source  of  protein  than  any  of  the  animal 
foods  except  cheese,  very  cheap  meat,  and  salt  fish.  At  usual  prices 
skim  milk  furnishes  protein  more  cheaply  than  any  common  animal 
food  except  salt  fish.  The  protein  of  vegetable  foods  is  less  expensive, 
but,  on  the  other  hand,  as  prepared  for  the  table  is  less  thoroughly 
digested.     Moreover,  it  is  accompanied  by  such  large  amounts  of 

363 


34 


THE   USE   OF    MILK  AS   FOOD. 


Chart  III. — Pecuniary  ecoriomy  of  milk  and  other  foods.  Amount  of  actual 
nutrients  obtained  in  di^erent  foods  for  10  cents  at  certain  assumed  prices 
per  pound. 


PROTEIN. 


/TtT. 


C^RBOMYDP/irES. 


FUEL  VALUE. 


303 


THE   USE   OF    MILp   AS   FOOD.  35 

carbohydrates  that  to  secure  much  vegetable  protein  in  the  diet 
usually  means  an  excess  of  the  carbohydrates.  Under  ordinary  mar- 
ket conditions  milk,  and  even  skim  milk,  is  a  cheaper  source  of  body 
fuel  than  any  of  the  usual  animal  foods  except  cheese  and  salt  pork, 
but  is  a  dearer  one  than  the  usual  vegetable  foods.  Here  again,  how- 
ever, the  milk  furnishes  the  ingredients  in  a  form  more  readily  and 
thoroughly  digested  than  the  vegetable  foods  as  ordinarily  served. 
Milk,  then,  is  fully  as  economical  a  source  of  nutrients  as  most  animal 
foods,  but  is  dearer  than  most  vegetable  foods.  It  has  the  decided 
advantage  of  having  no  waste,  requiring  no  time  for  preparation,  and 
being  more  digestible  than  the  vegetable  foods.  Skim  milk  answers 
the  most  important  purposes  of  milk  in  the  ordinary  mixed  diet,  and 
under  usual  market  conditions  costs  at  most  only  half  as  much  as 
whole  milk.  Both  whole  and  skim  milk  at  moderate  prices  arc  there- 
fore to  be  ranked  among  the  most  economical  of  our  foods,  not  only 
when  taken  as  beverages,  but  also  when  used  in  preparing  other  foods. 

THE  TJSE  OF  MILK  IN  COOKING. 

If  freely  used  in  the  preparation  of  other  foods,  milk  can  be  made 
to  add  considerably  to  the  food  value  of  the  meals.  Many  dishes 
are,  of  course,  richer  in  flavor  if  whole  milk  is  used  rather  than 
skimmed,  but  for  the  purpose  of  increasing  the  food  value  of  the  diet 
the  main  nutritive  ingredient — that  is,  the  nitrogenous  material — as 
we  have  seen,  is  in  the  skim  milk ;  if  the  extra  fat  is  needed,  it  may  be 
supplied  in  the  form  of  butter,  which  is  usually  a  more  economical 
source  than  whole  milk,  or  in  the  form  of  lard  or  other  culinary  fat. 

Most  persons  consider  that  the  choice  between  bread  made  with 
milk  and  that  made  with  water  depends  simply  upon  the  taste  and 
appearance.  There  is,  however,  a  difference  in  the  food  value,  as 
will  be  seen  from  figures  showing  the  average  composition  of  various 
foods  prepared  with  milk  and  of  similar  dishes  in  which  it  is  not  used. 
According  to  the  figures  which  were  taken  from  anal3'ses  made  at  the 
University  of  Minnesota,*  bread  made  with  skim  milk  is  richer  in 
total  solids,  protein,  and  fats  than  otherwise  similar  bread  made 
with  water.  The  dilTerences  are  not  very  great,  but  they  are  well 
worth  considering,  especially  where  skim  milk  is  a  drug  in  the  mar- 
ket. The  importance  of  skim  milk  in  bread  making  has  also  been 
demonstrated  experimentally  at  the  Maine  Experiment  Station. 

Milk  soups  furnish  an  excellent  means  of  increasing  the  food  value 
of  a  meal  or  of  using  up  superfluous  milk.  Sometimes  the  milk  is 
mixed  wdth  "  stock  "  made  from  meat,  and  sometimes,  as  in  vegetable 
purees,  it  forms  the  basis  to  which  the  pulp  of  some  vegetable,  such 
as  beans,  peas,  potatoes,  corn,  or  celery,  is  added  to  give  flavor  and 

«  U.  S.  Dept.  Agr.,  Office  Expt.  Stas.  Bui.  G7, 
363 


36  THE   USE    QF    MILK   AS   FOOD. 

"  b(x]y."     Oyster  stew  made  with  milk  owes  its  food  value  more  to 
the  milk  than  to  the  oysters. 

]Milk  01*  ''  white  "'  and  '"  cream  "  sauces  are  also  very  useful,  not 
only  for  the  nutritive  material  they  supply  but  also  as  a  help  in 
using  up  '•  left  overs."  Bits  of  meat  can  often  be  made  very  attrac- 
tive by  serving  them  on  toast  minced  and  "  creamed,"  and  many 
warmed-over  vegetables  are  improved  by  the  addition  of  milk  or 
white  sauce,  while  the  same  sauce  also  helps  in  giving  variety  in 
winter  when  not  many  kinds  of  vegetables  are  to  be  had.  There  is 
almost  no  end  to  the  puddings  and  desserts  in  which  considerable 
milk  is  used.  Blanc  mange  is  practically  flavored  milk,  jellied  with 
starch,  Irish  moss,  or  some  similar  material,  and  the  simplest  kinds 
of  ice  cream  are  milk  and  cream  mixtures  flavored  and  frozen. 
Junket  is  simply  milk  curd  separated  by  rennet,  as  in  cheese  making, 
and  eaten  before  the  bacteria  which  give  the  cheese  its  flavor  develop. 
Then  there  are  all  the  puddings  made  of  some  form  of  cereal  and 
milk  and  flavored  in  some  way,  as  bread  puddings,  cornstarch,  rice, 
and  tapioca  jouddings,  and  the  countless  forms  of  custard  of  which 
milk  and  eggs  make  the  basis.  Almost  all  of  these,  if  carefully  made, 
are  nutritious,  easily  digested,  and  economical.  For  children  and 
persons  of  weak  digestion  the  simpler  ones  like  blanc  mange,  corn- 
starch, and  rice  puddings  are  almost  indispensable. 

MILK  PRODUCTS. 
BUTTER  AND   CHEESE. 

These  are  by  far  the  most  important  products  of  the  dairy  industry, 
but  so  much  has  been  written  of  them  in  other  publications  of  this 
Department  that  they  need  only  be  mentioned  briefly  here. 

Chart  IV  shows  in  graphic  form  the  composition  of  butter,  cheese, 
and  other  milk  products.  The  data  are  given  in  tabular  form  for 
these  and  other  foods  on  page  9. 

Butter,  which  is  practically  separated  milk  fat,  is  one  of  the 
most  important  sources  of  fat  in  our  diet  and  certainly  the  most 
palatable  and  one  of  the  most  digestible.  Its  flavor  depends  upon 
such  factors  as  volatile  fats,  cleanliness,  the  action  of  bacteria,  and 
the  amount  of  salt  added.  The  price  varies  greatly,  even  during  the 
same  season,  and  is  influenced  by  flavor,  color,  texture,  etc.  These 
factors  affect  quality  rather  than  composition,  and  so  far  as  is  known 
have  little  effect  on  nutritive  value  or  digestibility.  As  has  been 
stated  already,  it  is  usually  a  cheaper  source  of  pure  fat  than  Whole 
milk.  The  butter  on  sale  in  the  United  States  is  usually  salted,  partly 
because  of  the  general  preference  for  the  salt  flavor  and  partly  be- 
cause of  improved  keeping  qualities.     It  is  noticeable  that  butter  is 

363 


THE   USE   OF    MILK   AS   FOOD. 


37 


now  less  heavily  salted  than  was  the  case  before  cold  storage  and 
other  such  conveniences  became  common.  In  Europe  sweet  or  un- 
salted  butter  is  very  popular,  and  its  popularity  is  growing  in  the 
United  States.  Such  butter  has  a  mild,  creamy  flavor,  which  verj'' 
many  relish.  As  it  does  not  keep  well  it  must  be  used  soon  after  it 
is  made,  and  ranks  as  a  delicacy.  Many  persons  make  sweet  butter 
at  home  as  needed,  using  for  the  purpose  an  egg  beater  or  one  of  the 
devices  similar  in  principle  which  are  on  the  market  for  this  purpose. 


Chart  IV. — Percentage  composition  and  fuel  value  per  pound  of  butter,  cheese, 

and  other  milJc  products. 

(The  constituents  arc  expressed  in  per  cent,  the  fuel  values  in  calories  per  pound.) 

CREAM  CHEESE 


BUTTER 


AVATeR:II.O      ^ FAT:8S.O 


K 


protein:  1.0^  MSH:3.0 

FUEL  VALUE:  FUEL  VALUE: 


^PROTEIN  :  25.9 


CAPBO - 
HYDRATES:  2.4 


3410     CALORIES  PER  POUND     COTTAGE   CHEESE  fQ^Q  CALORIES  PER  POUND 

CARBOHYDRATES :  4.3 


/NFANT  FOODS      fat- i.o^ '^protein :20.9 


(milk   and    starches)  fuel  VALUE: 


WAT£R:4.3-^^ -^  /PR0TEIN:9.6 

FAT:3.S 


ASH:  2.1- 


M/LH  POWDER 
DRIED    SHIM   MILK 


WATER:3.0 


510  CALORIES  PER  POUND 

FAT:  3.1 


J  ^ARBO- 

1'^  HYDRATES:  60.2 


ASHie.O 


1780  CALORIES  PER  POUND 


xPROTEIN:  34.0 


^CARBO- 
r    HYDRATES:  51.9 


/7/S  CALORIES  PER  POUND 


A  peculiar  form  of  butter,  called  "  ghee,"  is  commonly  used  in  India 
and  central  Asia.  The  water  is  boiled  out  from  freshly  made  but- 
ter and  the  resulting  product  is  kept  for  general  use,  especially  in 
cooking.  In  the  cold,  high  regions  of  Tibet  it  is  used  in  large  quan- 
tities, lumps  of  it  being  put  even  into  tea.  This  product  is  very 
similai:  to  the  rendered  butter  which  is  used  by  orthodox  Jews  in 
kosher  cookery.  Rendered  butter  is  also  a  common  culinary  fat  in 
Egypt  and  some  other  countries. 

363 


38  THE   USE    OF    MILK   AS   FOOD. 

Cheese  consists  of  the  casein  of  the  milk  and  more  or  less  of  the  fat 
and  mineral  matters  which  are  precipitated  along  Avith  it  when  rennet 
is  added  to  milk.  Thqre  are  countless  varieties  made  not  only  from 
cow's  milk  but  also  from  that  of  goats,  ewes,  and  other  animals.  The 
flavor  is  due  chiefly  to  the  action  of  ferments,  of  bacteria,  or  of  molds. 
The  changes  which  these  agents  induce  are  now  well  understood,  and 
the  manufacture  of  cheese  of  different  types  is  an  important  industry 
in  which  the  expert  cheese  maker  now  utilizes  them  according  to 
scientific  methods  to  bring  about  the  desired  results  with  almost  un- 
varying certainty.  The  literature  of  food  and  nutrition  contains  lit- 
tle definite  information  regarding  the  digestibility  of  cheese,  but 
there  is  a  general  opinion  that  this  food,  particularly  the  very  strong 
varieties,  is  less  easily  digested  than  most  milk  products.  As  regards 
thoroughness  of  digestion,  a  very  large  number  of  digestion  experi- 
ments carried  on^by  the  Office  of  Experiment  Stations  in  cooperation 
with  the  Bureau  of  Animal  Industry  of  the  Department  of  Agricul- 
ture have  shown  that,  when  consumed  even  in  relatively  large 
amounts,  cheese  is  very  thoroughly  assimilated.  Furthermore,  it 
caused  no  physiological  disturbances  in  the  large  number  of  tests  in 
which  it  was  used.  Cheese,  containing,  as  it  does,  almost  all  of  the 
protein  and  fat  of  the  milk  from  which  it  is  made  and  having  a  com- 
paratively low  water  content,  is  a  very  nutritious  food,  and  the, 
cheaper  kinds  may  well  be  used  more  abundantly  than  is  commonly 
the  case  in  this  country  as  a  part  of  the  regular  diet  and  not  simply 
as  a  condiment  at  the  end  of  the  hearty  meal.  The  cost  of  cheese 
varies  greatly  with  the  kind,  but  the  higher  prices  are  usually  paid 
for  distinctive  flavors  or  texture  rather  than  for  food  values. 

JUNKET. 

A  favorite  dish  for  invalid  dietetics  and  for  more  general  use  is 
prepared  by  adding  rennet  to  milk  and  allowing  it  to  stand  undis- 
turbed until  it  thickens  or  coagulates — that  is,  until  the  casein  is 
precipitated.  If  the  process  is  carefully  carried  out  a  thick,  custard- 
like product  results.  If,  however,  it  is  stirred  the  casein  readily 
breaks  up  and  separates  from  the  whey.  There  are  a  number  of 
preparations  of  rennet  on  the  market  designed  especially  for  making 
junket,  all  of  which  seem  to  give  satisfactory  results. 

COTTAGE   CHEESE. 

Cottage  cheese  as  commonly  made  at  home  from  sour  milk  with  or 
without  the  cream  is  a  nutritious  and  palatable  food,  as  may  be  seen 
from  figures  for  its  composition  in  the  table  on  page  9,  and  the  data 
given  in  Chart  IV,  page  37.  Under  ordinary  conditions  it  is  very 
inexpensive.     There  are  several  sorts  of  this  cheese  on  the  market 

363 


THE  USE   OF   MILK  AS   FOOD.  39 

which  are  made  in  large  quantities  as  regidar  commercial  products 
and  sold  under  such  names  as  Neufchatel,  or,  less  commonly,  cream 
cheese.  In  many  city  markets  the  homemade  product  may  also  be 
purchased.  Cottage  cheese  is  used  as  a  palatable  addition  to  the 
diet,  alone  or  seasoned  in  various  ways,  and  is  also  used  in  the 
prej)aration  of  a  number  of  dishes. 

CREAM. 

Cream  is  made  up  principally  of  water  and  the  fat  of  milk,  but 
contains  also  a  little  protein,  carbohydrates,  and  mineral  matters. 
When  served  with  cereals,  fruit,  etc.,  it  not  only  improves  the  flavor, 
but  adds  to  the  nutritive  value  of  the  dish.  When  added  to  the  cus- 
tards, cakes,  soups,  and  other  food  it  materially  increases  the  fat  con- 
tent and  makes  the  dish  "  richer,"  as  does  cream,  either  plain  or 
whipped,  served  with  a  dessert  dish  or  other  food. 

Judging  by  available  data,  cream  in  large  quantities  is  less  easily 
digested  than  the  same  amount  of  whole  milk,  because  it  contains  so 
much  fat ;  but,  on  the  other  hand,  it  is  more  thoroughly  digested  than 
most  other  forms  of  fat,  and  is  often  ordered  by  ph3^sicians  when 
tlie  amount  of  this  ingredient  in  the  diet  is  to  be  increased.  At  usual 
prices  it  is  so  expensive  that  it  must  be  considered  a  luxury  to  most 
people  who  purchase  their  milk  and  cream. 

When  cream  is  beaten  or  whipped  the  fine  bubbles  formed  do  not 
break  readily,  so  that  it  may  be  whipped  until  it  is  stiff,  almost  like 
egg  white.  If  the  "  whipping  "  is  too  long  continued  the  fat  globules 
separate,  and  butter  results.  If  cream  is  too  thin  it  does  not  whip 
well,  and  the  same  may  be  said  of  very  thick  cream.  Several  ex- 
planations of  this  property  of  "  whipping  "  have  been  offered,  but  it 
seems  fair  to  say  that  no  entirely  satisfactory  explanation  has  been 
given.  That  the  property  may  be  dependent  upon  the  calcium  con- 
tent of  the  milk  is  suggested  by  the  fact  that  cream  to  which  a  small 
amount  of  a  solution  of  lime  in  sugar  and  water  has  been  added 
may  be  readily  whipped.  This  question  has  been  carefully  studied 
at  the  Wisconsin  Station,  and  it  was  found  that  if  a  small  portion  of 
such  a  lime  solution  was  added  to  pasteurized  cream  which  ordinarily 
does  not  whip  readily,  or  to  thin  cream,  satisfactory  results  could  be 
obtained. 

A  cream  product  known  as  "  Devonshire  clotted  cream,"  or  simply 
as  "  clotted  cream,"  and  very  popular  in  Great  Britain  and,  to  a  less 
extent,  elsewhere,  is  made  by  allowing  pans  of  milk  to  stand  undis- 
turbed in  a  cool  place  until  cream  rises  and  then  scalding,  care  being 
taken  not  to  disturb  the  cream  on  top  af  tlie  milk.  When  this  is 
properly  done  and  the  pans  allowed  to  cool,  the  cream  may  be  taken 
off  in  a  thick,  clotted  condition,  and  is  ready  for  use.  It  has  a 
peculiar,  nutty  flavor,  which  most  persons  relish. 

363 


40  THE   USE   OF    MILK   AS   FOOD. 

BUTTERMILK. 

Besides  skim  millv,  there  is  another  important  by-product  resulting 
from  the  manufacture  of  butter,  namely,  buttermilk.  In  butter  mak- 
ing the  fat  globules  are  brought  together  by  churning  and  removed, 
leaving  a  thin  liquid.  This  buttermilk  is  very  like  skim  milk  in  com- 
position, but  it  has  usually  a  mild  acid  taste,  because  the  cream  is 
generally  allowed  to  sour  before  churning.  Buttermilk  is  often  used 
as  a  beverage,  and  has  much  the  same  food  value  as  skim  milk.  An 
ordinary  ghiss  would  contain  about  as  much  nourishment  as  2  ounces 
of  bread,  a  good-sized  potato,  or  a  half  pint  of  oysters.  To  many 
jDersons  buttermilk  is  as  palatable,  or  even  more  palatable,  than  whole 
or  skim  milk,  but  others  find  the  sour  taste  very  unpleasant.  This 
sour  taste  is  due  mainly  to  lactic  acid,  and  does  not  make  the  butter- 
milk less  digestible.  On  the  contrary,  its  casein  forms  a  more  flaky 
curd  than  that  of  ordinary  milk.  Buttermilk  is  frequently  fed  to 
babies,  especially  in  Holland,  and  is  sometimes  prescribed  when  the 
protein  of  ordinary  milk  proves  indigestible.  Its  general  use  is 
increasing  in  this  country.  Buttermilk  ice  cream  is  considered  a 
delicacy  in  some  sections,  especially  for  invalids. 

Condensed  buttermilk  is  manufactured  to  some  extent,  but  seems 
to  be  best  known  in  Europe,  and  is  certainly  not  common  even  there. 

WHEY. 

Just  as  buttermilk  represents  the  residue  of  milk  from  butter  mak- 
ing, so  whey  represents  what  is  left  from  cheese  making,  and  consists 
mainly  of  water,  milk  sugar,  and  mineral  matters.  It  is  less  nutritious 
than  skim  milk  and  buttermilk,  but  is  occasionally  useful  as  a  mild 
laxative  drink  for  invalids.  In  the  "  whey  cures  "  for  dyspeptics, 
of  Avhicli  so  much  was  heard  some  years  ago,  whey  was  usually  com- 
bined with  a  simple  vegetable  diet  and  the  beneficial  results  were 
probably  due  as  much  to  the  simple,  out-of-door  life,  which  made 
part  of  the  treatment,  as  to  the  whey  itself. 

T\niey  may  be  made  at  home  by  cooking  sweet  milk  with  some  acid 
material,  such  as  vinegar,  lemon  juice,  sour  wine,  or  cream  of  tartar, 
or  even  with  sour  milk.  Such  whey  differs  but  little  in  composition 
from  regular  cheese  whey.  Fresh  curds  and  whej  is  an  old-fashioned 
dish  still  used  to  some  extent,  though  less  common  than  it  was  when 
cheese  making  was  regularly  carried  on  as  a  home  industry. 

SOUR  MILK   OR  CLABBER. 

Sour  milk  or  clabber  is  a  common  article  of  diet  in  many  parts  of 
the  United  States  and  is  wholesome,  and  to  those  who  care  for  it 
very  refreshing  and  palatable.    It  is  certainly  nutritious,  since  when 

363 


THE   USE   OF   MILK    AS   FOOD.  41 

made  from  whole  milk  it  contains  all  the  nutritive  ingredients  origi- 
nally present,  and  when  only  skim  milk  is  used  it  contains  the  casein 
and  other  constituents  except  the  fat.  Usually  no  special  methods  are 
followed  to  prepare  sour  milk  or  clabber  for  table  use,  though  most 
housewives  recognize  the  fact  that  if  the  souring  takes  place  too 
slowly  the  clabber  may  have  a  bitter  or  unpleasant  flavor.  This  is, 
of  course,  due  to  the  develoj^ment  of  undesirable  bacteria  along  with 
those  which  cause  the  souring  of  the  milk.  Sour  milk  is  much  used 
in  cookery,  and  adds  materially  to  the  nutritive  value  of  the  dish 
of  which  it  forms  a  part.  Before  baking  powders  became  so  com- 
mon sour  milk  and  baking  soda  were  very  commonly  used  to  leaven 
doughs  and  batters  of  various  sorts.  Some  cooks  maintain  that  they 
can  secure  the  best  results  by  using  only  the  whey  of  sour  milk,  but 
this  naturally  gives  a  less  nutritious  dish  and  therefore  is  not  so 
desirable. 

KEPHIR,  KOUMISS,  AND  OTHER  FERMENTED  MILK  PRODUCTS. 

Since  earliest  times  fermented-milk  products  have  been  used  as 
beverages  and  articles  of  diet  in  Central  Asia,  Turkey,  and  other 
countries.  These  products  are  prepared  by  allowing  special  ferments 
or  yeasts  to  develop  in  milk,  and  like  all  fermented  beverages  owe 
their  sparkling  or  effervescent  qualities  to  the  carbon  dioxid  j^ro- 
duced  by  the  action  of  organisms.  The  flavor  differs  with  the  process 
of  manufacture.  These  fermented-milk  beverages  have  proved  very 
satisfactory  in  invalid  dietetics  and  are  now  well  known  and  com- 
monly used.  Fermented-milk  beverages  may  be  made  at  home,  but 
are  perhaps  more  commonly  commercial  products  in  the  United 
States.  In  this  country  cow's  milk  is  almost  universally  used  to 
make  these  beverages,  but  other  milk,  for  instance,  mare's  milk,  is 
more  common  in  Central  Asia  and  other  regions. 

A  carbonated  milk,  which  is  made  by  charging  milk  with  carbon 
dioxid,  is  sometimes  found  on  sale,  but,  of  course,  lacks  the  special 
qualities  which  all  the  fermented  products  contain. 

Some  of  these  fermented-milk  products  contain  lactic  acid  forming 
bacteria  in  great  abundance,  and  their  extensive  use  has  been  much 
discussed  recently,  owing  to  the  prominence  which  has  been  given 
to  the  theory  that  very  many  diseases,  particularly  those  incident  to 
old  age,  are  the  results  of  the  development  of  putrefactive  bacteria 
in  the  intestine  and  the  possibilities  of  hindering  the  growth  of  such 
organisms  by  the  presence  of  lactic  acid.  The  most  recent  observa- 
tions, however,  make  it  doubtful  whether  it  is  as  beneficial  as  has  been 
claimed  by  some  enthusiasts, 

363 


42  THE   USE   OF    MILK   AS   FOOD. 

STJMMAEY. 

Some  idea  of  the  importance  of  milk  as  human  food  may  be  gained 
from  the  fact  that  about  one-sixth  of  the  total  food  of  the  average 
family  is  furnished  by  it  and  its  products.  Milk  from  various  mam- 
mals is  used  in  various  parts  of  the  world,  but  with  us  that  of  the 
cow  so  far  surpasses  all  other  kinds  in  importance  that  imless  other- 
wise specified  the  w  ord  "  milk  "  is  taken  to  refer  to  cow's  milk  only. 
Few  staple  foods  vary  so  much  in  composition,  but,  on  the  average, 
good,  unadulterated  milk  should  contain  about  87  fter  cent  water  and 
13  per  cent  solids.  About  one-fourth  of  these  solids  are  furnished 
by  the  protein  compounds,  casein,  and  albumin,  the  casein  being  five 
or  six  times  more  abundant  than  the  albumin.  Fats  (butter  fat) 
form  one-third  of  the  total  solids.  Butter  fat  occurs  in  globules 
throughout  the  milk,  and  it  is  upon  the  size  and  number  of  them  that 
the  creaminess  of  milk  depends.  The  larger  the  globules  the  more 
easily  and  completely  will  they  rise  as  cream  to  the  surface  of  the 
milk.  Carbohydrates  make  up  38  per  cent  of  the  solids,  by  far  the 
most  important  of  them  being  lactose,  or  milk  sugar.  The  remain- 
ing 5  per  cent  of  solids  consists  of  mineral  matters,  the  bulk  of  which 
are  phosi:)hates  and  chlorids  of  soda,  potash,  and  lime. 

Besides  these  chemical  constituents,  milk  almost  inevitably  con- 
tains bacteria  of  many  kinds  and  in  varying  numbers.  They  cause 
the  souring  of  milk  and  the  ripening  of  cream  and  cheese,  and  pro- 
duce many  other  changes  in  the  appearance  and  flavor.  The  numl)er 
present  in  freshly-drawTi  milk  varies  enormously  with  the  conditions 
of  milking,  and,  as  they  are  greatly  increased  with  dirty  and  careless 
handling,  cleanliness  in  all  matters  pertaining  to  the  milking  and 
marketing  of  milk  and  keeping  it  in  the  home  can  not  be  too  strongly 
insisted  on.  Disease  germs,  notably  those  of  typhoid,  diphtheria, 
scarlet  fever,  and  tuberculosis,  may  also  be  carried  in  milk,  so  that 
the  purity  of  the  milk  supply  is  of  vital  importance  to  every  family 
and  community. 

Although  some  of  the  bacteria  in  milk  are  essential  in  the  manu- 
facture of  butter  and  cheese,  they  are  as  a  class  a  source  of  danger 
to  the  ordinary  consumer.  Without  them  milk  would  stay  sweet 
indefinitely,  and  the  problem  of  keeping  milk  is  simply  one  of  check- 
ing their  growth.  The  less  there  are  in  the  fresh  milk,  the  slighter 
the  danger,  hence  the  superior  keeping  qualities  of  milk  from  a  clean, 
well-ordered  dairy.  Tliey  are  comparatively  inactive  at  a  tempera- 
ture below  50°  F.,  and  therefore  milk  should  be  kept  in  a  cool  place. 
Freezing  does  not  kill  bacteria  and  produces  undesirable  changes  in 
the  milk.  Extreme  heat  does  kill  them,  but  also  produces  other  un- 
desirable changes.  Nevertheless,  heat  is  employed  to  preserve  milk 
in  the  two  common  methods  of  pasteurization  and  sterilization.     In 

3G3 


THE  USE  OP  MILK  AS  FOOD.  43 

the  former  the  aim  is  to  apply  heat  in  such  a  way  as  to  kill  the  most 
bacteria  without  producing  the  undesirable  changes;  in  the  latter, 
to  apply  enough  heat  to  kill  all  the  bacteria,  but  with  the  least  pos- 
sible undesirable  change.  Bacteria  require  moisture  as  well  as  heat' 
for  their  growth,  therefore  by  extracting  the  water,  as  in  condensed 
milk,  milk  powders,  etc.,  milk  may  be  preserved  indefinitely.  An- 
other way  of  keeping  it  is  by  the  use  of  chemicals  to  kill  the  bacteria, 
but  as  such  chemicals  may  be  injurious  to  human  beings  as  well, 
such  practices  are  not  usually  to  be  recommended. 

AVliat  is  commonly  known  as  the  richness  of  milk  depends  upon 
the  amount  of  fat.  This  varies  so  greatly  in  milk  from  different 
animals  and  is  so  easily  reduced  by  a  fraudulent  dealer  that  many 
efforts  have  been  made  to  regulate  the  price  of  milk  according  to  its 
fat  content.  Milk  graded  according  to  government  standards  is 
sold  in  some  cities,  especially  in  Europe.  Certified  milk — that  is, 
milk  in  sealed  jars  from  establisliments  regularly  inspected — is  more 
commonly  known  in  this  country,  and  rightly  commands  a  higher 
price  than  that  from  uncertain  sources.  Of  course,  cleanliness  and 
care  are  as  important  in  keeping  milk  in  the  home  as  in  the  dairy  and 
market,  and  each  housekeeper  should  see  to  it  that  all  receptacles  in 
which  it  is  kept  are  thoroughly  scalded  each  time  they  are  used;  if 
this  is  neglected,  bacteria  from  the  old  milk  will  contaminate  the 
fresh. 

Compared  with  other  food  materials,  milk  furnishes  the  nutritive 
ingredients  in  forms  in  which  they  may  be  easily  and  thoroughly 
digested  by  the  normal,  healthy  person,  and  often  by  those  of  im- 
paired health.  Boiling  is  believed  by  many  to  make  the  protein 
slightly  less  digestible,  but  as  yet  knowledge  on  this  point  is  incom- 
plete. The  digestibility  of  the  fat  seems  to  depend  upon  the  size  of 
the  globules,  the  smaller  ones  being  more  easily  absorbed.  This  ex- 
plains why  rich,  "  creamy  "  milk,  such  as  that  given  by  the  Channel 
breeds,  sometimes  causes  digestive  trouble  in  children. 

Mother's  milk  is  best  adapted  by  nature  to  the  nourishment  of  in- 
fants, and  differs  from  cow's  milk  mainly  in  the  character  of  its  pro- 
tein, in  the  smaller  size  of  its  fat  globules,  and  in  its  greater  amount 
of  milk  sugar.  "N^Tien  necessary,  cow's  milk  may  be  artificially  modi- 
fied to  approach  it  more  nearly  in  composition,  but  the  results  are 
not  always  satisfactory,  especially  as  regards  the  protein. 

Milk  contains  too  much  water  to  be  a  perfect  food  for  adults; 
nevertheless,  its  solids  furnish  all  the  necessary  ingredients  and  in 
good  proportions.  A  large  glass  of  it  yields  as  much  nourishment 
as  a  slice  of  i:oast  beef. 

Unless  exceptionally  high  prices  are  paid  for  it,  milk  is  fully  as 
economical  a  source  of  nutrients  as  other  animal  foods,  but  dearer 

3G3 


44  THE   USE   OF    MILK   AS   FOOD. 

than  most  staple  A^egotable  products.  It  should  be  borne  in  mind, 
however,  that  it  requires  no  preparation,  has  no  waste,  and  is  more 
thoroughly  digested  than  most  vegetable  foods.  As  a  source  of  pro- 
tein, the  most  expensive  of  the  nutritive  ingredients,  it  is  especially 
economical.  Skim  milk,  which  is  whole  milk  minus  part  of  its  fat, 
and  which  costs  only  half  as  much  as  whole  milk,  furnishes  protein 
about  four  times  as  cheaply  as  beef,  and  since  fat  is  usually  abundant 
in  the  ordinary  mixed  diet  might  most  advantageously  be  used  in  the 
place  of  whole  milk  in  dietaries  where  cost  must  be  carefully  con- 
sidered. The  freer  use  of  skim  milk  in  cooking  is  also  to  be  recom- 
mended. Of  course,  foods  prepared  with  either  skim  or  whole  milk 
are  by  so  much  the  more  nutritious  than  those  prepared  with  water. 

Butter  and  cheese  are  the  most  important  milk  products.  Butter 
is  one  of  the  chief  sources  of  fat  in  the  ordinary  diet  and  furnishes 
it  in  a  very  palatable  and  easily  digested  form.  Cheese  consists  of 
the  casein  of  milk  plus  more  or  less  of  the  fat  and  mineral  matters. 
The  flavor  and  texture  of  the  many  varieties  are  due  mainly  to  the 
peculiar  bacteria  and  ferments  which  the  various  methods  of  manu- 
facture develop.  The  less  expensive  varieties  make  one  of  the  cheap- 
est sources  of  protein,  and  might  well  be  more  freely  used  as  part  of 
the  regular  diet.  Digestion  experiments  indicate  that  the  common 
and  milder  varieties  are  more  easily  and  thoroughly  assimilated  than 
is  som.etimes  supposed.  The  other  milk  products — junket,  whej^  but- 
termilk, clabber,  and  the  fermented  forms,  such  as  kephir  and 
koumiss — are  all  nutritious  foods  and  are  often  of  especial  value  in 
invalid  diet.  In  short,  milk  and  its  products  are  fully  entitled  to 
their  prominent  place  in  our  food  list  as  comparatively  inexpensive, 
easily  digested  sources  of  all  the  necessary  ingredients  of  our  diet. 


[A  list  giving  the  titles  of  all  Farmers'  Bulletins  available  for  distribution  will  be 
Beat  free  upon  application  to  a  Member  of  Congress  or  the  Secretary  of  Agriculture.] 
303 

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